diff --git a/README.md b/README.md
index caf1dc71d..2105de7ba 100644
--- a/README.md
+++ b/README.md
@@ -19,10 +19,35 @@ Find out more:
 >
 > | Package | Use it for |
 > |---------|------------|
-> | `Ably.PubSub.Device` | End-user device applications (desktop, mobile, Unity, MAUI, browser-adjacent clients) — *added in the next PR in this stack* |
-> | `Ably.PubSub.Server` | Server-side and backend applications — *added in the next PR in this stack* |
+> | `Ably.PubSub.Device` | End-user device applications (desktop, mobile, Unity, MAUI, browser-adjacent clients) |
+> | `Ably.PubSub.Server` | Server-side and backend applications (ASP.NET, Azure hosts, workers, console apps) |
 > | `Ably.PubSub.Core` | Internal implementation shared by the two packages above. Not intended for direct use; you receive it transitively |
 >
+> Install the package for the side your code runs on, and create clients through that package's factory methods — **they are the supported entry points**. `Ably.PubSub.Core` is internal: a client constructed directly from `AblyRealtime` or `AblyRest` is not classified as device-side or server-side, which Ably's platform behaviour and billing depend on.
+>
+> ```sh
+> dotnet add package Ably.PubSub.Server
+> ```
+>
+> ```csharp
+> using IO.Ably.PubSub.Server;
+>
+> var realtime = PubSubServer.CreateRealtimeClient("<API_KEY>");
+> var http = PubSubServer.CreateHttpClient("<API_KEY>");
+> ```
+>
+> ```sh
+> dotnet add package Ably.PubSub.Device
+> ```
+>
+> ```csharp
+> using IO.Ably.PubSub.Device;
+>
+> var realtime = PubSubDevice.CreateClient("<API_KEY>");
+> ```
+>
+> Each factory also takes a `ClientOptions` or an `Action<ClientOptions>`. The returned clients are the ordinary `AblyRealtime` and `AblyRest`, so the whole of the `IO.Ably` API remains available — including device-side connectionless operations such as message history, presence reads and token requests, which is why the device package has one door and no separate HTTP factory.
+>
 > The compiled assembly is now `Ably.PubSub.Core.dll`. The code namespace is unchanged: `using IO.Ably;` and every public type name stay as they are for now.
 >
 > Today's [`ably.io`](https://www.nuget.org/packages/ably.io) 1.x package is unaffected and continues from a 1.x maintenance branch for a year after 2.0 becomes generally available; it is never published from this branch again. The same applies to `ably.io.push.android` and `ably.io.push.ios`, whose Xamarin-era projects are not part of the 2.0 set (see [PushNotifications.md](./PushNotifications.md)).
@@ -30,8 +55,6 @@ Find out more:
 > Never reference `ably.io` and `Ably.PubSub.*` from the same project: they share the `IO.Ably` namespace, so mixing them is a compile error by design.
 >
 > This also applies **transitively**. NuGet dedupes only by package ID, so a graph that pulls both `ably.io` 1.x (often via a library dependency) and any `Ably.PubSub.*` package loads *both* assemblies, and every `IO.Ably.*` type then exists twice: you get compile error CS0433 where your own code names those types, and runtime type-identity failures (`InvalidCastException`-class) where a library exposes `IO.Ably` types across its API. There is no type-forwarding between the packages. Detect it with `dotnet nuget why <project> ably.io`; if a dependency genuinely forces both, isolate them with an [`extern alias`](https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/extern-alias) — note `<Aliases>` applies only to a **direct** `PackageReference`, so first promote `ably.io` to a direct reference of the affected project, then add `<Aliases>ablyLegacy</Aliases>` to it and `extern alias ablyLegacy;` in the consuming file — otherwise treat a both-packages graph as unsupported and migrate the transitive dependency off `ably.io`.
->
-> The Installation and Usage sections below still describe the 1.x `ably.io` package; they are replaced with `Ably.PubSub.Device`/`Ably.PubSub.Server` instructions before 2.0 general availability.
 
 ---
 
@@ -62,18 +85,18 @@ Everything you need to get started with Ably:
 
 ## Installation
 
-The SDK is available as a [nuget package](https://www.nuget.org/packages/ably.io/). To get started with your project, install the package from the Package Manager Console or the .NET CLI.
+Install the package for the side your application runs on. Server-side and backend applications use `Ably.PubSub.Server`; end-user device applications (desktop, mobile, Unity, MAUI) use `Ably.PubSub.Device`. Both bring in `Ably.PubSub.Core` transitively — never install `Ably.PubSub.Core` directly.
 
-Package Manager Console:
+Server-side (.NET CLI):
 
 ```shell
-PM> Install-Package ably.io
+dotnet add package Ably.PubSub.Server
 ```
 
-.NET CLI in your project directory:
+Device-side (.NET CLI):
 
 ```shell
-dotnet add package ably.io
+dotnet add package Ably.PubSub.Device
 ```
 
 ### MAUI configuration
@@ -95,8 +118,11 @@ Add the following to your `.csproj` file to prevent trimming of the Ably assembl
 The following code connects to Ably's realtime messaging service, subscribes to a channel to receive messages, and publishes a test message to that same channel:
 
 ```csharp
-// Initialize Ably Realtime client
-var realtime = new AblyRealtime("your-ably-api-key");
+// Initialize an Ably Realtime client through the server-side door
+using IO.Ably.PubSub.Server;
+
+var realtime = PubSubServer.CreateRealtimeClient("your-ably-api-key");
+// Device-side applications use: PubSubDevice.CreateClient("your-ably-api-key");
 
 // Wait for connection to be established
 realtime.Connection.On(ConnectionEvent.Connected, args =>
@@ -175,5 +201,5 @@ var websocketOptions = new MsWebSocketOptions
 
 options.TransportFactory = new MsWebSocketTransport.TransportFactory(websocketOptions);
 
-var realtime = new AblyRealtime(options);
+var realtime = PubSubServer.CreateRealtimeClient(options);
 ```
diff --git a/cake-build/helpers/tools.cake b/cake-build/helpers/tools.cake
index 4241f4042..92db1d4a4 100644
--- a/cake-build/helpers/tools.cake
+++ b/cake-build/helpers/tools.cake
@@ -11,7 +11,7 @@ public class ILRepackHelper
         _context = context;
     }
     
-    public void MergeDLLs(FilePath primaryDll, FilePath[] dllsToMerge, FilePath outputDll)
+    public void MergeDLLs(FilePath primaryDll, FilePath[] dllsToMerge, FilePath outputDll, FilePath internalizeExcludeFile = null)
     {
         if (!_context.FileExists(primaryDll))
         {
@@ -56,7 +56,9 @@ public class ILRepackHelper
         // Build ILRepack arguments - explicitly merge only the DLLs we specify
         var args = new ProcessArgumentBuilder()
             .Append("/targetplatform:v4")
-            .Append("/internalize")
+            .Append(internalizeExcludeFile != null && _context.FileExists(internalizeExcludeFile)
+                ? $"/internalize:\"{internalizeExcludeFile.FullPath}\""
+                : "/internalize")
             // /lib: Specifies where ILRepack should search for referenced assemblies when loading the primary DLL.
             // This is needed because Mono.Cecil (used by ILRepack) must resolve all type references while reading
             // the assembly metadata, even before the merge begins. Without this, it fails to resolve types from
@@ -66,6 +68,23 @@ public class ILRepackHelper
             .Append($"/keyfile:\"{rootDir.CombineWithFilePath("IO.Ably.snk").FullPath}\"")
             .Append("/parallel")
             .Append($"/out:\"{outputDll.FullPath}\"");
+
+        // When ILRepack runs under Mono (macOS/Linux), the netstandard2.0 inputs' 'netstandard'
+        // facade lives in Mono's 4.5/Facades directory, which /targetplatform:v4 does not search;
+        // add it as an extra /lib so Mono.Cecil can resolve it. No-op on Windows (paths absent).
+        var monoFacadesCandidates = new[]
+        {
+            new DirectoryPath("/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/4.5/Facades"),
+            new DirectoryPath("/usr/lib/mono/4.5/Facades")
+        };
+        foreach (var facades in monoFacadesCandidates)
+        {
+            if (_context.DirectoryExists(facades))
+            {
+                args.Append($"/lib:\"{facades.FullPath}\"");
+                break;
+            }
+        }
         
         // Add all DLL paths explicitly (primary + merging DLLs)
         foreach (var dllPath in dllPaths)
diff --git a/cake-build/tasks/build.cake b/cake-build/tasks/build.cake
index d4b554da6..435edd971 100644
--- a/cake-build/tasks/build.cake
+++ b/cake-build/tasks/build.cake
@@ -81,7 +81,7 @@ Task("_Build_Ably_Unity_Dll")
     .Description("Create merged Unity DLL with all dependencies")
     .Does(() =>
 {
-    Information("Merging Unity dependencies into Ably.PubSub.Core.dll...");
+    Information("Merging Unity dependencies and the Ably.PubSub.Device door into Ably.PubSub.Device.dll...");
     
     var netStandard20BinPath = paths.Src
         .Combine("Ably.PubSub.Core")
@@ -108,8 +108,19 @@ Task("_Build_Ably_Unity_Dll")
         throw new Exception($"Newtonsoft.Json.dll not found at: {newtonsoftDll}");
     }
     
+    var deviceDoorDll = paths.Src
+        .Combine("Ably.PubSub.Device")
+        .Combine("bin/Release/netstandard2.0")
+        .CombineWithFilePath("Ably.PubSub.Device.dll");
+
+    if (!FileExists(deviceDoorDll))
+    {
+        throw new Exception($"Device door DLL not found: {deviceDoorDll}. Please build the Ably.PubSub.Device project first.");
+    }
+
     var dllsToMerge = new[]
     {
+        deviceDoorDll,
         netStandard20BinPath.CombineWithFilePath("IO.Ably.DeltaCodec.dll"),
         netStandard20BinPath.CombineWithFilePath("System.Runtime.CompilerServices.Unsafe.dll"),
         netStandard20BinPath.CombineWithFilePath("System.Threading.Channels.dll"),
@@ -118,7 +129,10 @@ Task("_Build_Ably_Unity_Dll")
     };
     
     var unityOutputPath = paths.Root.Combine("unity/Assets/Ably/Plugins");
-    var outputDll = unityOutputPath.CombineWithFilePath("Ably.PubSub.Core.dll");
+    // The merged Unity plugin is named after the public device door package; the
+    // primary input stays Ably.PubSub.Core.dll (its public API survives the merge)
+    // and the real Ably.PubSub.Device.dll is one of the merged, exclude-protected inputs.
+    var outputDll = unityOutputPath.CombineWithFilePath("Ably.PubSub.Device.dll");
     
     // Delete existing output DLL if it exists
     if (FileExists(outputDll))
@@ -127,8 +141,9 @@ Task("_Build_Ably_Unity_Dll")
         Information($"Deleted existing DLL: {outputDll}");
     }
     
-    // Merge all dependencies into primary DLL in one go
-    ilRepackHelper.MergeDLLs(primaryDll, dllsToMerge, outputDll);
+    // Merge all dependencies into primary DLL in one go, keeping the device door namespace public
+    var internalizeExclude = paths.Root.Combine("cake-build").CombineWithFilePath("unity-internalize-exclude.txt");
+    ilRepackHelper.MergeDLLs(primaryDll, dllsToMerge, outputDll, internalizeExclude);
     
     Information($"✓ Unity DLL created at: {outputDll}");
 });
diff --git a/cake-build/tasks/package.cake b/cake-build/tasks/package.cake
index a9c18afcf..54e17ac9a 100644
--- a/cake-build/tasks/package.cake
+++ b/cake-build/tasks/package.cake
@@ -35,11 +35,13 @@ Task("_Package_Create_NuGet")
     Information($"Creating NuGet packages version {version}...");
 
     // The lockstep package set. Every package here is built from this repository
-    // and released at the same version. Stack PR 2 adds the door packages
-    // (ably.pubsub.device.nuspec, ably.pubsub.server.nuspec) to this list.
+    // and released at the same version, and both door packages pin the core exactly.
+    // Packed core-first so the order matches the publish order stack PR 3 adds.
     var nuspecFiles = new[]
     {
-        "nuget/ably.pubsub.core.nuspec"
+        "nuget/ably.pubsub.core.nuspec",
+        "nuget/ably.pubsub.device.nuspec",
+        "nuget/ably.pubsub.server.nuspec"
     };
 
     var nugetSettings = new NuGetPackSettings
@@ -133,7 +135,7 @@ Task("_Package_Unity")
 ///////////////////////////////////////////////////////////////////////////////
 
 Task("Package")
-    .Description("Create the NuGet packages (Ably.PubSub.Core)")
+    .Description("Create the NuGet packages (Ably.PubSub.Core, Ably.PubSub.Device, Ably.PubSub.Server)")
     .IsDependentOn("_Package_Create_NuGet");
 
 Task("UnityPackage")
diff --git a/cake-build/unity-internalize-exclude.txt b/cake-build/unity-internalize-exclude.txt
new file mode 100644
index 000000000..45af4c34f
--- /dev/null
+++ b/cake-build/unity-internalize-exclude.txt
@@ -0,0 +1 @@
+^IO\.Ably\.PubSub\.Device\..*
diff --git a/examples/NotificationsPublisher/NotificationsPublisher.csproj b/examples/NotificationsPublisher/NotificationsPublisher.csproj
index 8a93d385f..a2a9bb85d 100644
--- a/examples/NotificationsPublisher/NotificationsPublisher.csproj
+++ b/examples/NotificationsPublisher/NotificationsPublisher.csproj
@@ -8,7 +8,7 @@
     </PropertyGroup>
 
     <ItemGroup>
-      <ProjectReference Include="..\..\src\Ably.PubSub.Core\Ably.PubSub.Core.csproj" />
+      <ProjectReference Include="..\..\src\Ably.PubSub.Server\Ably.PubSub.Server.csproj" />
         <PackageReference Include="StyleCop.Analyzers" Version="1.1.118">
             <PrivateAssets>all</PrivateAssets>
             <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
diff --git a/examples/NotificationsPublisher/Program.cs b/examples/NotificationsPublisher/Program.cs
index 981fae502..56bb4a36d 100644
--- a/examples/NotificationsPublisher/Program.cs
+++ b/examples/NotificationsPublisher/Program.cs
@@ -2,6 +2,7 @@
 using System.IO;
 using System.Text;
 using IO.Ably;
+using IO.Ably.PubSub.Server;
 using IO.Ably.Types;
 using Newtonsoft.Json.Linq;
 using Terminal.Gui;
@@ -284,7 +285,7 @@ void InitialiseAbly(string key)
                     LogLevel = LogLevel.Warning,
                     AutoConnect = false
                 };
-                Ably = new AblyRealtime(options);
+                Ably = PubSubServer.CreateRealtimeClient(options);
             }
 
             var key = GetCurrentKey();
diff --git a/nuget/ably.pubsub.device.nuspec b/nuget/ably.pubsub.device.nuspec
new file mode 100644
index 000000000..d6a8e2e18
--- /dev/null
+++ b/nuget/ably.pubsub.device.nuspec
@@ -0,0 +1,50 @@
+<?xml version="1.0" encoding="utf-8"?>
+<package xmlns="http://schemas.microsoft.com/packaging/2013/05/nuspec.xsd">
+    <metadata>
+        <id>Ably.PubSub.Device</id>
+        <version>$version$</version>
+        <title>Ably.PubSub.Device</title>
+        <authors>Martin Georgiev, Sachin Shinde, Yavor Ivanov, Jack Rutherford, Tom Kirby-Green</authors>
+        <owners>Ably Real-time Ltd</owners>
+        <license type="expression">Apache-2.0</license>
+        <projectUrl>https://github.com/ably/ably-dotnet</projectUrl>
+        <icon>icon.png</icon>
+        <readme>README.md</readme>
+        <requireLicenseAcceptance>false</requireLicenseAcceptance>
+        <description>The supported entry point for Ably Pub/Sub in an end-user device application - a mobile or desktop app, a Unity game, a set-top box or any other client the end user holds. Create clients through PubSubDevice.CreateClient(...) in the IO.Ably.PubSub.Device namespace; it accepts an API key, an Ably token, a ClientOptions or an Action&lt;ClientOptions&gt;, and returns the ordinary AblyRealtime so the whole of the IO.Ably API remains available, including device-side connectionless operations such as message history, presence reads and token requests. Creating a client any other way - including directly from the Ably.PubSub.Core implementation package this depends on - does not classify it as device-side, which Ably's platform behaviour and billing depend on. Install Ably.PubSub.Server instead in a server-side application. See https://www.ably.com for more info.</description>
+        <releaseNotes>https://github.com/ably/ably-dotnet/releases</releaseNotes>
+        <copyright>©2026 Ably Real-time Ltd</copyright>
+        <tags>ably realtime messaging websocket pubsub presence device mobile dotnet csharp maui unity netstandard</tags>
+        <repository type="git" url="https://github.com/ably/ably-dotnet.git" branch="main" />
+        <language />
+        <!-- The exact pin is the NuGet analogue of ably-js's exact peerDependencies: the door and
+             the core are released in lockstep, and consumers must never resolve two core
+             versions. nuget.exe substitutes $version$ inside the dependency version attribute, so
+             the packed pin equals the package version (asserted by the PackagingSpecs pre-flight
+             and release-dry-run in the release tooling PR). -->
+        <dependencies>
+          <group targetFramework="netstandard2.0">
+            <dependency id="Ably.PubSub.Core" version="[$version$]" />
+          </group>
+          <group targetFramework="net6.0">
+            <dependency id="Ably.PubSub.Core" version="[$version$]" />
+          </group>
+          <group targetFramework="net7.0">
+            <dependency id="Ably.PubSub.Core" version="[$version$]" />
+          </group>
+        </dependencies>
+    </metadata>
+    <files>
+        <file src="..\src\Ably.PubSub.Device\bin\$configuration$\netstandard2.0\Ably.PubSub.Device.dll" target="lib\netstandard2.0" />
+        <file src="..\src\Ably.PubSub.Device\bin\$configuration$\netstandard2.0\Ably.PubSub.Device.pdb" target="lib\netstandard2.0" />
+        <file src="..\src\Ably.PubSub.Device\bin\$configuration$\netstandard2.0\Ably.PubSub.Device.xml" target="lib\netstandard2.0" />
+        <file src="..\src\Ably.PubSub.Device\bin\$configuration$\net6.0\Ably.PubSub.Device.dll" target="lib\net6.0" />
+        <file src="..\src\Ably.PubSub.Device\bin\$configuration$\net6.0\Ably.PubSub.Device.pdb" target="lib\net6.0" />
+        <file src="..\src\Ably.PubSub.Device\bin\$configuration$\net6.0\Ably.PubSub.Device.xml" target="lib\net6.0" />
+        <file src="..\src\Ably.PubSub.Device\bin\$configuration$\net7.0\Ably.PubSub.Device.dll" target="lib\net7.0" />
+        <file src="..\src\Ably.PubSub.Device\bin\$configuration$\net7.0\Ably.PubSub.Device.pdb" target="lib\net7.0" />
+        <file src="..\src\Ably.PubSub.Device\bin\$configuration$\net7.0\Ably.PubSub.Device.xml" target="lib\net7.0" />
+        <file src="..\README.md" target="README.md" />
+        <file src="..\images\logo.png" target="icon.png" />
+    </files>
+</package>
diff --git a/nuget/ably.pubsub.server.nuspec b/nuget/ably.pubsub.server.nuspec
new file mode 100644
index 000000000..34417e59a
--- /dev/null
+++ b/nuget/ably.pubsub.server.nuspec
@@ -0,0 +1,56 @@
+<?xml version="1.0" encoding="utf-8"?>
+<package xmlns="http://schemas.microsoft.com/packaging/2013/05/nuspec.xsd">
+    <metadata>
+        <id>Ably.PubSub.Server</id>
+        <version>$version$</version>
+        <title>Ably.PubSub.Server</title>
+        <authors>Martin Georgiev, Sachin Shinde, Yavor Ivanov, Jack Rutherford, Tom Kirby-Green</authors>
+        <owners>Ably Real-time Ltd</owners>
+        <license type="expression">Apache-2.0</license>
+        <projectUrl>https://github.com/ably/ably-dotnet</projectUrl>
+        <icon>icon.png</icon>
+        <readme>README.md</readme>
+        <requireLicenseAcceptance>false</requireLicenseAcceptance>
+        <description>The supported entry point for Ably Pub/Sub in a server-side application - an ASP.NET or Azure host, a worker, a console app or any other backend the end user does not hold. Create clients through PubSubServer.CreateRealtimeClient(...) and PubSubServer.CreateHttpClient(...) in the IO.Ably.PubSub.Server namespace; each accepts an API key, an Ably token, a ClientOptions or an Action&lt;ClientOptions&gt;, and returns the ordinary AblyRealtime or AblyRest so the whole of the IO.Ably API remains available. Creating a client any other way - including directly from the Ably.PubSub.Core implementation package this depends on - does not classify it as server-side, which Ably's platform behaviour and billing depend on. Install Ably.PubSub.Device instead in an end-user device application. See https://www.ably.com for more info.</description>
+        <releaseNotes>https://github.com/ably/ably-dotnet/releases</releaseNotes>
+        <copyright>©2026 Ably Real-time Ltd</copyright>
+        <tags>ably realtime messaging websocket pubsub presence server backend dotnet csharp aspnet netstandard</tags>
+        <repository type="git" url="https://github.com/ably/ably-dotnet.git" branch="main" />
+        <language />
+        <!-- The exact pin is the NuGet analogue of ably-js's exact peerDependencies: the door and
+             the core are released in lockstep, and consumers must never resolve two core
+             versions. nuget.exe substitutes $version$ inside the dependency version attribute, so
+             the packed pin equals the package version (asserted by the PackagingSpecs pre-flight
+             and release-dry-run in the release tooling PR). -->
+        <dependencies>
+          <group targetFramework="net46">
+            <dependency id="Ably.PubSub.Core" version="[$version$]" />
+          </group>
+          <group targetFramework="netstandard2.0">
+            <dependency id="Ably.PubSub.Core" version="[$version$]" />
+          </group>
+          <group targetFramework="net6.0">
+            <dependency id="Ably.PubSub.Core" version="[$version$]" />
+          </group>
+          <group targetFramework="net7.0">
+            <dependency id="Ably.PubSub.Core" version="[$version$]" />
+          </group>
+        </dependencies>
+    </metadata>
+    <files>
+        <file src="..\src\Ably.PubSub.Server.NETFramework\bin\$configuration$\Ably.PubSub.Server.dll" target="lib\net46" />
+        <file src="..\src\Ably.PubSub.Server.NETFramework\bin\$configuration$\Ably.PubSub.Server.pdb" target="lib\net46" />
+        <file src="..\src\Ably.PubSub.Server.NETFramework\bin\$configuration$\Ably.PubSub.Server.xml" target="lib\net46" />
+        <file src="..\src\Ably.PubSub.Server\bin\$configuration$\netstandard2.0\Ably.PubSub.Server.dll" target="lib\netstandard2.0" />
+        <file src="..\src\Ably.PubSub.Server\bin\$configuration$\netstandard2.0\Ably.PubSub.Server.pdb" target="lib\netstandard2.0" />
+        <file src="..\src\Ably.PubSub.Server\bin\$configuration$\netstandard2.0\Ably.PubSub.Server.xml" target="lib\netstandard2.0" />
+        <file src="..\src\Ably.PubSub.Server\bin\$configuration$\net6.0\Ably.PubSub.Server.dll" target="lib\net6.0" />
+        <file src="..\src\Ably.PubSub.Server\bin\$configuration$\net6.0\Ably.PubSub.Server.pdb" target="lib\net6.0" />
+        <file src="..\src\Ably.PubSub.Server\bin\$configuration$\net6.0\Ably.PubSub.Server.xml" target="lib\net6.0" />
+        <file src="..\src\Ably.PubSub.Server\bin\$configuration$\net7.0\Ably.PubSub.Server.dll" target="lib\net7.0" />
+        <file src="..\src\Ably.PubSub.Server\bin\$configuration$\net7.0\Ably.PubSub.Server.pdb" target="lib\net7.0" />
+        <file src="..\src\Ably.PubSub.Server\bin\$configuration$\net7.0\Ably.PubSub.Server.xml" target="lib\net7.0" />
+        <file src="..\README.md" target="README.md" />
+        <file src="..\images\logo.png" target="icon.png" />
+    </files>
+</package>
diff --git a/src/Ably.PubSub.Device/Ably.PubSub.Device.csproj b/src/Ably.PubSub.Device/Ably.PubSub.Device.csproj
new file mode 100644
index 000000000..3bdcfeff3
--- /dev/null
+++ b/src/Ably.PubSub.Device/Ably.PubSub.Device.csproj
@@ -0,0 +1,61 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <!-- The core's TFMs minus net462 (PDR-091b plan decision 5b): there is no net462 Device
+         head, and .NET Framework is not a supported device target. -->
+    <TargetFrameworks>netstandard2.0;net6.0;net7.0</TargetFrameworks>
+    <CodeAnalysisRuleSet>..\IO.Ably.ruleset</CodeAnalysisRuleSet>
+    <Configurations>Debug;Release;package</Configurations>
+    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <AssemblyName>Ably.PubSub.Device</AssemblyName>
+    <RootNamespace>IO.Ably.PubSub.Device</RootNamespace>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(MSBuildRuntimeType)'=='Mono'">
+    <TargetFramework>netstandard2.0</TargetFramework>
+  </PropertyGroup>
+
+  <!-- Signed under package builds only, in lockstep with Ably.PubSub.Core: a consumer of the
+       signed core must never have to mix signed and unsigned Ably assemblies, and the plain
+       (non-Package) builds keep everything unsigned so the core's keyless
+       InternalsVisibleTo test access keeps compiling. -->
+  <PropertyGroup Condition="'$(Package)'=='True'">
+    <SignAssembly>true</SignAssembly>
+    <AssemblyOriginatorKeyFile>..\..\IO.Ably.snk</AssemblyOriginatorKeyFile>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='package|AnyCPU'">
+    <OutputPath>bin\package</OutputPath>
+  </PropertyGroup>
+
+  <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+
+  <PropertyGroup Condition=" '$(Configuration)' == 'Release' ">
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="..\CommonAssemblyInfo.cs" Link="Properties\CommonAssemblyInfo.cs" />
+    <!-- Shared source, compiled into both door assemblies rather than published. -->
+    <Compile Include="..\Ably.PubSub.Side\Side.cs" Link="Side.cs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <AdditionalFiles Include="..\stylecop.json" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="StyleCop.Analyzers" Version="1.1.118">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Ably.PubSub.Core\Ably.PubSub.Core.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/Ably.PubSub.Device/PubSubDevice.cs b/src/Ably.PubSub.Device/PubSubDevice.cs
new file mode 100644
index 000000000..d12f1d312
--- /dev/null
+++ b/src/Ably.PubSub.Device/PubSubDevice.cs
@@ -0,0 +1,70 @@
+using System;
+using IO.Ably.PubSub.Internal;
+
+namespace IO.Ably.PubSub.Device
+{
+    /// <summary>
+    /// Entry point for Ably Pub/Sub applications that run on an end-user device - a mobile or
+    /// desktop app, a Unity game, a set-top box or any other client the end user holds.
+    /// <para>
+    /// This factory is the only supported way to create a client from this package. The
+    /// Ably.PubSub.Core package that carries the implementation is an internal dependency: a
+    /// client constructed directly from <see cref="AblyRealtime"/> or <see cref="AblyRest"/> is
+    /// not classified as device-side, which Ably's platform behaviour and billing depend on.
+    /// </para>
+    /// <para>
+    /// There is one door by design, and it returns the ordinary <see cref="AblyRealtime"/>, so
+    /// the whole of the <c>IO.Ably</c> API remains available. Device-side connectionless
+    /// operations - message history, presence reads, token requests and
+    /// <c>Request</c>/<c>RequestV2</c> - are available on that client through its
+    /// <see cref="AblyRealtime.RestClient"/> and channel APIs, so per PDR-091 there is
+    /// deliberately no device HTTP door.
+    /// </para>
+    /// <para>
+    /// The API-key overload is kept on purpose: per PDR-091, device-side API keys stay allowed
+    /// at launch and enforcement is server-side. Token authentication remains the recommended
+    /// scheme for anything the end user holds.
+    /// </para>
+    /// </summary>
+    public static class PubSubDevice
+    {
+        /// <summary>
+        /// Creates a realtime client for an end-user device from an API key or an Ably token.
+        /// </summary>
+        /// <param name="keyOrToken">
+        /// A valid Ably API key (of the form <c>APP_ID.KEY_ID:KEY_SECRET</c>) or an Ably token.
+        /// The core applies the same colon rule its own constructors use to tell them apart.
+        /// </param>
+        /// <returns> A connected-on-demand realtime client. </returns>
+        public static AblyRealtime CreateClient(string keyOrToken)
+        {
+            return CreateClient(new ClientOptions(keyOrToken));
+        }
+
+        /// <summary>
+        /// Creates a realtime client for an end-user device from a set of client options.
+        /// </summary>
+        /// <param name="options"> The client options. </param>
+        /// <returns> A connected-on-demand realtime client. </returns>
+        /// <exception cref="ArgumentNullException"> Thrown when <paramref name="options"/> is null. </exception>
+        public static AblyRealtime CreateClient(ClientOptions options)
+        {
+            // The core constructor is [Obsolete] to steer consumers to the doors; this door is
+            // the sanctioned caller, constructing the client from the side-stamped copy.
+#pragma warning disable CS0618
+            return new AblyRealtime(Side.WithSideAgent(options, Side.DeviceAgentIdentifier));
+#pragma warning restore CS0618
+        }
+
+        /// <summary>
+        /// Creates a realtime client for an end-user device, configured by the supplied action.
+        /// </summary>
+        /// <param name="configure"> Action that populates the client options. </param>
+        /// <returns> A connected-on-demand realtime client. </returns>
+        /// <exception cref="ArgumentNullException"> Thrown when <paramref name="configure"/> is null. </exception>
+        public static AblyRealtime CreateClient(Action<ClientOptions> configure)
+        {
+            return CreateClient(Side.Configure(configure));
+        }
+    }
+}
diff --git a/src/Ably.PubSub.NetFramework.sln b/src/Ably.PubSub.NetFramework.sln
index 48a9db1b7..538bff444 100644
--- a/src/Ably.PubSub.NetFramework.sln
+++ b/src/Ably.PubSub.NetFramework.sln
@@ -32,14 +32,9 @@ Project("{D954291E-2A0B-460D-934E-DC6B0785DB48}") = "Ably.PubSub.Tests.Shared",
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IO.Ably.DeltaCodec", "..\lib\delta-codec\IO.Ably.DeltaCodec\IO.Ably.DeltaCodec.csproj", "{EEAD196C-8D90-4402-9EAC-273F0DF5EFCB}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ably.PubSub.Server.NETFramework", "Ably.PubSub.Server.NETFramework\Ably.PubSub.Server.NETFramework.csproj", "{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}"
+EndProject
 Global
-	GlobalSection(SharedMSBuildProjectFiles) = preSolution
-		Ably.PubSub.Tests.Shared\Ably.PubSub.Tests.Shared.projitems*{1609f12c-8216-4e7c-ade0-240bfe160242}*SharedItemsImports = 13
-		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{2d265650-b1ec-4f8d-b043-a2e3dcc23fd8}*SharedItemsImports = 4
-		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{3553e1b2-8f1f-4e83-9524-08e702c14fcf}*SharedItemsImports = 13
-		Ably.PubSub.Tests.Shared\Ably.PubSub.Tests.Shared.projitems*{567feef7-41af-42f2-ad34-546a278355b1}*SharedItemsImports = 4
-		Ably.PubSub.Shared.MsgPack\Ably.PubSub.Shared.MsgPack.projitems*{eebf3249-3ca3-4078-a188-f8b916c3f4c2}*SharedItemsImports = 13
-	EndGlobalSection
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		AppStore|Any CPU = AppStore|Any CPU
 		AppStore|ARM = AppStore|ARM
@@ -266,6 +261,70 @@ Global
 		{EEAD196C-8D90-4402-9EAC-273F0DF5EFCB}.Release|x64.Build.0 = Release|Any CPU
 		{EEAD196C-8D90-4402-9EAC-273F0DF5EFCB}.Release|x86.ActiveCfg = Release|Any CPU
 		{EEAD196C-8D90-4402-9EAC-273F0DF5EFCB}.Release|x86.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.AppStore|Any CPU.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.AppStore|Any CPU.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.AppStore|ARM.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.AppStore|ARM.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.AppStore|x64.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.AppStore|x64.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.AppStore|x86.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.AppStore|x86.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.CI_Release|Any CPU.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.CI_Release|Any CPU.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.CI_Release|ARM.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.CI_Release|ARM.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.CI_Release|x64.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.CI_Release|x64.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.CI_Release|x86.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.CI_Release|x86.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug 4.0|Any CPU.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug 4.0|Any CPU.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug 4.0|ARM.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug 4.0|ARM.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug 4.0|x64.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug 4.0|x64.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug 4.0|x86.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug 4.0|x86.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|ARM.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|ARM.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x64.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x86.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package_netstandard|Any CPU.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package_netstandard|Any CPU.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package_netstandard|ARM.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package_netstandard|ARM.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package_netstandard|x64.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package_netstandard|x64.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package_netstandard|x86.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package_netstandard|x86.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package|Any CPU.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package|Any CPU.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package|ARM.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package|ARM.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package|x64.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package|x64.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package|x86.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.package|x86.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release 4.0|Any CPU.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release 4.0|Any CPU.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release 4.0|ARM.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release 4.0|ARM.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release 4.0|x64.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release 4.0|x64.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release 4.0|x86.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release 4.0|x86.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|Any CPU.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|ARM.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|ARM.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x64.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x64.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x86.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -277,8 +336,16 @@ Global
 		{EEBF3249-3CA3-4078-A188-F8B916C3F4C2} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
 		{1609F12C-8216-4E7C-ADE0-240BFE160242} = {C2F43DB7-AAA0-4687-9897-5D686EC91245}
 		{EEAD196C-8D90-4402-9EAC-273F0DF5EFCB} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {F69D4156-FC22-4B8E-AD72-2A7323D42CC4}
 	EndGlobalSection
+	GlobalSection(SharedMSBuildProjectFiles) = preSolution
+		Ably.PubSub.Tests.Shared\Ably.PubSub.Tests.Shared.projitems*{1609f12c-8216-4e7c-ade0-240bfe160242}*SharedItemsImports = 13
+		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{2d265650-b1ec-4f8d-b043-a2e3dcc23fd8}*SharedItemsImports = 4
+		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{3553e1b2-8f1f-4e83-9524-08e702c14fcf}*SharedItemsImports = 13
+		Ably.PubSub.Tests.Shared\Ably.PubSub.Tests.Shared.projitems*{567feef7-41af-42f2-ad34-546a278355b1}*SharedItemsImports = 4
+		Ably.PubSub.Shared.MsgPack\Ably.PubSub.Shared.MsgPack.projitems*{eebf3249-3ca3-4078-a188-f8b916c3f4c2}*SharedItemsImports = 13
+	EndGlobalSection
 EndGlobal
diff --git a/src/Ably.PubSub.NetStandard.sln b/src/Ably.PubSub.NetStandard.sln
index 4d31bce31..d77ab7eb8 100644
--- a/src/Ably.PubSub.NetStandard.sln
+++ b/src/Ably.PubSub.NetStandard.sln
@@ -30,12 +30,11 @@ Project("{D954291E-2A0B-460D-934E-DC6B0785DB48}") = "Ably.PubSub.Tests.Shared",
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IO.Ably.DeltaCodec", "..\lib\delta-codec\IO.Ably.DeltaCodec\IO.Ably.DeltaCodec.csproj", "{D8CAACFA-FE6E-46BC-9B23-8AA3B2055125}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ably.PubSub.Device", "Ably.PubSub.Device\Ably.PubSub.Device.csproj", "{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ably.PubSub.Server", "Ably.PubSub.Server\Ably.PubSub.Server.csproj", "{882D22FB-68CB-4EA7-AE62-B79F7165854D}"
+EndProject
 Global
-	GlobalSection(SharedMSBuildProjectFiles) = preSolution
-		Ably.PubSub.Tests.Shared\Ably.PubSub.Tests.Shared.projitems*{1609f12c-8216-4e7c-ade0-240bfe160242}*SharedItemsImports = 13
-		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{3553e1b2-8f1f-4e83-9524-08e702c14fcf}*SharedItemsImports = 13
-		Ably.PubSub.Shared.MsgPack\Ably.PubSub.Shared.MsgPack.projitems*{eebf3249-3ca3-4078-a188-f8b916c3f4c2}*SharedItemsImports = 13
-	EndGlobalSection
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		AppStore|Any CPU = AppStore|Any CPU
 		AppStore|ARM = AppStore|ARM
@@ -262,6 +261,134 @@ Global
 		{D8CAACFA-FE6E-46BC-9B23-8AA3B2055125}.Release|x64.Build.0 = Release|Any CPU
 		{D8CAACFA-FE6E-46BC-9B23-8AA3B2055125}.Release|x86.ActiveCfg = Release|Any CPU
 		{D8CAACFA-FE6E-46BC-9B23-8AA3B2055125}.Release|x86.Build.0 = Release|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.AppStore|Any CPU.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.AppStore|Any CPU.Build.0 = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.AppStore|ARM.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.AppStore|ARM.Build.0 = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.AppStore|x64.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.AppStore|x64.Build.0 = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.AppStore|x86.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.AppStore|x86.Build.0 = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.CI_Release|Any CPU.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.CI_Release|Any CPU.Build.0 = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.CI_Release|ARM.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.CI_Release|ARM.Build.0 = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.CI_Release|x64.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.CI_Release|x64.Build.0 = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.CI_Release|x86.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.CI_Release|x86.Build.0 = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.Debug 4.0|Any CPU.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.Debug 4.0|Any CPU.Build.0 = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.Debug 4.0|ARM.ActiveCfg = Debug|Any CPU
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B}.Debug 4.0|ARM.Build.0 = Debug|Any CPU
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+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.AppStore|x86.ActiveCfg = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.AppStore|x86.Build.0 = Debug|Any CPU
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+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Debug 4.0|Any CPU.Build.0 = Debug|Any CPU
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+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Debug 4.0|x64.Build.0 = Debug|Any CPU
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+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Debug|x86.Build.0 = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package_netstandard|Any CPU.ActiveCfg = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package_netstandard|Any CPU.Build.0 = Debug|Any CPU
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+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package_netstandard|ARM.Build.0 = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package_netstandard|x64.ActiveCfg = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package_netstandard|x64.Build.0 = Debug|Any CPU
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+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package_netstandard|x86.Build.0 = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package|Any CPU.ActiveCfg = package|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package|Any CPU.Build.0 = package|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package|ARM.ActiveCfg = package|Any CPU
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+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package|x64.Build.0 = package|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package|x86.ActiveCfg = package|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.package|x86.Build.0 = package|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release 4.0|Any CPU.ActiveCfg = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release 4.0|Any CPU.Build.0 = Debug|Any CPU
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+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release 4.0|x64.Build.0 = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release 4.0|x86.ActiveCfg = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release 4.0|x86.Build.0 = Debug|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release|ARM.ActiveCfg = Release|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release|ARM.Build.0 = Release|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release|x64.ActiveCfg = Release|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release|x64.Build.0 = Release|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release|x86.ActiveCfg = Release|Any CPU
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -273,8 +400,15 @@ Global
 		{4805A9DA-3412-4BE8-8B95-5A0EFDA1AC01} = {C2F43DB7-AAA0-4687-9897-5D686EC91245}
 		{1609F12C-8216-4E7C-ADE0-240BFE160242} = {C2F43DB7-AAA0-4687-9897-5D686EC91245}
 		{D8CAACFA-FE6E-46BC-9B23-8AA3B2055125} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
+		{ADD94C3B-7F88-4D5E-8C64-9FC84DC1DC0B} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
+		{882D22FB-68CB-4EA7-AE62-B79F7165854D} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {F69D4156-FC22-4B8E-AD72-2A7323D42CC4}
 	EndGlobalSection
+	GlobalSection(SharedMSBuildProjectFiles) = preSolution
+		Ably.PubSub.Tests.Shared\Ably.PubSub.Tests.Shared.projitems*{1609f12c-8216-4e7c-ade0-240bfe160242}*SharedItemsImports = 13
+		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{3553e1b2-8f1f-4e83-9524-08e702c14fcf}*SharedItemsImports = 13
+		Ably.PubSub.Shared.MsgPack\Ably.PubSub.Shared.MsgPack.projitems*{eebf3249-3ca3-4078-a188-f8b916c3f4c2}*SharedItemsImports = 13
+	EndGlobalSection
 EndGlobal
diff --git a/src/Ably.PubSub.Package.sln b/src/Ably.PubSub.Package.sln
index 1a0336f87..a2f4a0c60 100644
--- a/src/Ably.PubSub.Package.sln
+++ b/src/Ably.PubSub.Package.sln
@@ -25,13 +25,13 @@ Project("{D954291E-2A0B-460D-934E-DC6B0785DB48}") = "Ably.PubSub.Shared.MsgPack"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IO.Ably.DeltaCodec", "..\lib\delta-codec\IO.Ably.DeltaCodec\IO.Ably.DeltaCodec.csproj", "{55FD7D98-585B-4304-9B3F-3F518DB5CBFF}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ably.PubSub.Device", "Ably.PubSub.Device\Ably.PubSub.Device.csproj", "{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ably.PubSub.Server", "Ably.PubSub.Server\Ably.PubSub.Server.csproj", "{181C023D-975C-430A-BB80-A0BC884D415C}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ably.PubSub.Server.NETFramework", "Ably.PubSub.Server.NETFramework\Ably.PubSub.Server.NETFramework.csproj", "{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}"
+EndProject
 Global
-	GlobalSection(SharedMSBuildProjectFiles) = preSolution
-		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{2d265650-b1ec-4f8d-b043-a2e3dcc23fd8}*SharedItemsImports = 4
-		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{3180aa9d-9800-4eb2-87f0-ada47e2fff3d}*SharedItemsImports = 4
-		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{3553e1b2-8f1f-4e83-9524-08e702c14fcf}*SharedItemsImports = 13
-		Ably.PubSub.Shared.MsgPack\Ably.PubSub.Shared.MsgPack.projitems*{eebf3249-3ca3-4078-a188-f8b916c3f4c2}*SharedItemsImports = 13
-	EndGlobalSection
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
 		Debug|ARM = Debug|ARM
@@ -91,6 +91,54 @@ Global
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 		{55FD7D98-585B-4304-9B3F-3F518DB5CBFF}.Release|x86.Build.0 = Release|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Debug|ARM.ActiveCfg = Debug|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Debug|ARM.Build.0 = Debug|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Debug|x64.Build.0 = Debug|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Debug|x86.Build.0 = Debug|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Release|Any CPU.Build.0 = Release|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Release|ARM.ActiveCfg = Release|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Release|ARM.Build.0 = Release|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Release|x64.ActiveCfg = Release|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Release|x64.Build.0 = Release|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Release|x86.ActiveCfg = Release|Any CPU
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1}.Release|x86.Build.0 = Release|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Debug|Any CPU.Build.0 = Debug|Any CPU
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+		{181C023D-975C-430A-BB80-A0BC884D415C}.Debug|ARM.Build.0 = Debug|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Debug|x64.Build.0 = Debug|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Debug|x86.Build.0 = Debug|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Release|Any CPU.Build.0 = Release|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Release|ARM.ActiveCfg = Release|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Release|ARM.Build.0 = Release|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Release|x64.ActiveCfg = Release|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Release|x64.Build.0 = Release|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Release|x86.ActiveCfg = Release|Any CPU
+		{181C023D-975C-430A-BB80-A0BC884D415C}.Release|x86.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
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+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|ARM.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x64.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x86.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|Any CPU.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|ARM.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|ARM.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x64.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x64.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x86.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -101,8 +149,17 @@ Global
 		{3553E1B2-8F1F-4E83-9524-08E702C14FCF} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
 		{EEBF3249-3CA3-4078-A188-F8B916C3F4C2} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
 		{55FD7D98-585B-4304-9B3F-3F518DB5CBFF} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
+		{EB66BFC4-CF1D-4FA0-9618-C04FF34A02C1} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
+		{181C023D-975C-430A-BB80-A0BC884D415C} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {F69D4156-FC22-4B8E-AD72-2A7323D42CC4}
 	EndGlobalSection
+	GlobalSection(SharedMSBuildProjectFiles) = preSolution
+		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{2d265650-b1ec-4f8d-b043-a2e3dcc23fd8}*SharedItemsImports = 4
+		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{3553e1b2-8f1f-4e83-9524-08e702c14fcf}*SharedItemsImports = 13
+		Ably.PubSub.Shared\Ably.PubSub.Shared.projitems*{48ea337f-ae7b-4001-bd8c-da1668fc6cbd}*SharedItemsImports = 5
+		Ably.PubSub.Shared.MsgPack\Ably.PubSub.Shared.MsgPack.projitems*{eebf3249-3ca3-4078-a188-f8b916c3f4c2}*SharedItemsImports = 13
+	EndGlobalSection
 EndGlobal
diff --git a/src/Ably.PubSub.Server.NETFramework/Ably.PubSub.Server.NETFramework.csproj b/src/Ably.PubSub.Server.NETFramework/Ably.PubSub.Server.NETFramework.csproj
new file mode 100644
index 000000000..7c90e6716
--- /dev/null
+++ b/src/Ably.PubSub.Server.NETFramework/Ably.PubSub.Server.NETFramework.csproj
@@ -0,0 +1,99 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- The .NET Framework head of the Server door, mirroring Ably.PubSub.Core.NETFramework. It
+     exists only so that ably.pubsub.server.nuspec has a lib/net46 asset to sit alongside the
+     core's, since the core still ships one (PDR-091b plan decision 5). There is deliberately no
+     equivalent Device head (decision 5b). -->
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="..\packages\Microsoft.CodeQuality.Analyzers.2.9.6\build\Microsoft.CodeQuality.Analyzers.props" Condition="Exists('..\packages\Microsoft.CodeQuality.Analyzers.2.9.6\build\Microsoft.CodeQuality.Analyzers.props')" />
+  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+  <PropertyGroup>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <ProjectGuid>{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}</ProjectGuid>
+    <OutputType>Library</OutputType>
+    <AppDesignerFolder>Properties</AppDesignerFolder>
+    <RootNamespace>IO.Ably.PubSub.Server</RootNamespace>
+    <AssemblyName>Ably.PubSub.Server</AssemblyName>
+    <TargetFrameworkVersion>v4.6.2</TargetFrameworkVersion>
+    <FileAlignment>512</FileAlignment>
+    <NuGetPackageImportStamp>
+    </NuGetPackageImportStamp>
+    <TargetFrameworkProfile />
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+    <DebugSymbols>true</DebugSymbols>
+    <DebugType>full</DebugType>
+    <Optimize>false</Optimize>
+    <OutputPath>bin\Debug\</OutputPath>
+    <DefineConstants>TRACE;DEBUG</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+    <CodeAnalysisRuleSet>..\IO.Ably.ruleset</CodeAnalysisRuleSet>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <DocumentationFile>bin\Debug\Ably.PubSub.Server.xml</DocumentationFile>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+    <DebugType>pdbonly</DebugType>
+    <Optimize>true</Optimize>
+    <OutputPath>bin\Release\</OutputPath>
+    <DefineConstants>TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <CodeAnalysisRuleSet>..\IO.Ably.ruleset</CodeAnalysisRuleSet>
+    <WarningLevel>4</WarningLevel>
+    <DocumentationFile>bin\Release\Ably.PubSub.Server.xml</DocumentationFile>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'package|AnyCPU'">
+    <OutputPath>bin\package\</OutputPath>
+    <DocumentationFile>bin\package\Ably.PubSub.Server.xml</DocumentationFile>
+  </PropertyGroup>
+  <!-- Signed under package builds only, matching the SDK-style Server head: the packed net46
+       Server references the Package-signed net46 core, and the plain NetFramework build stays
+       all-unsigned. -->
+  <PropertyGroup Condition="'$(Package)'=='True'">
+    <SignAssembly>true</SignAssembly>
+    <AssemblyOriginatorKeyFile>..\..\IO.Ably.snk</AssemblyOriginatorKeyFile>
+  </PropertyGroup>
+  <!-- Fix for DeterministicSourcePaths in CI environments -->
+  <!-- See: https://github.com/dotnet/sourcelink/issues/572 -->
+  <ItemGroup>
+    <SourceRoot Include="$(MSBuildThisFileDirectory)..\..\"/>
+  </ItemGroup>
+  <ItemGroup>
+    <Reference Include="System" />
+    <Reference Include="System.Core" />
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="..\CommonAssemblyInfo.cs">
+      <Link>Properties\CommonAssemblyInfo.cs</Link>
+    </Compile>
+    <Compile Include="..\Ably.PubSub.Side\Side.cs">
+      <Link>Side.cs</Link>
+    </Compile>
+    <Compile Include="..\Ably.PubSub.Server\PubSubServer.cs">
+      <Link>PubSubServer.cs</Link>
+    </Compile>
+    <Compile Include="Properties\AssemblyInfo.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+    <AdditionalFiles Include="..\stylecop.json" />
+  </ItemGroup>
+  <ItemGroup>
+    <Analyzer Include="..\packages\Microsoft.CodeQuality.Analyzers.2.9.6\analyzers\dotnet\cs\Humanizer.dll" />
+    <Analyzer Include="..\packages\StyleCop.Analyzers.1.1.118\analyzers\dotnet\cs\StyleCop.Analyzers.CodeFixes.dll" />
+    <Analyzer Include="..\packages\StyleCop.Analyzers.1.1.118\analyzers\dotnet\cs\StyleCop.Analyzers.dll" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\Ably.PubSub.Core.NETFramework\Ably.PubSub.Core.NETFramework.csproj">
+      <Project>{2d265650-b1ec-4f8d-b043-a2e3dcc23fd8}</Project>
+      <Name>Ably.PubSub.Core.NETFramework</Name>
+    </ProjectReference>
+  </ItemGroup>
+  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
+    <PropertyGroup>
+      <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
+    </PropertyGroup>
+    <Error Condition="!Exists('..\packages\Microsoft.CodeQuality.Analyzers.2.9.6\build\Microsoft.CodeQuality.Analyzers.props')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Microsoft.CodeQuality.Analyzers.2.9.6\build\Microsoft.CodeQuality.Analyzers.props'))" />
+  </Target>
+</Project>
diff --git a/src/Ably.PubSub.Server.NETFramework/Properties/AssemblyInfo.cs b/src/Ably.PubSub.Server.NETFramework/Properties/AssemblyInfo.cs
new file mode 100644
index 000000000..b36bc208b
--- /dev/null
+++ b/src/Ably.PubSub.Server.NETFramework/Properties/AssemblyInfo.cs
@@ -0,0 +1,16 @@
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+// General Information about an assembly is controlled through the following
+// set of attributes. Change these attribute values to modify the information
+// associated with an assembly.
+[assembly: AssemblyTitle("Ably.PubSub.Server")]
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+[assembly: AssemblyDescription("Server-side entry point for Ably Pub/Sub")]
+
+// The following GUID is for the ID of the typelib if this project is exposed to COM
+[assembly: Guid("7b3c1f42-9d5e-4a87-b1c6-2e4f8a9d0b31")]
+
+[assembly: ComVisible(false)]
diff --git a/src/Ably.PubSub.Server.NETFramework/packages.config b/src/Ably.PubSub.Server.NETFramework/packages.config
new file mode 100644
index 000000000..8cf75130b
--- /dev/null
+++ b/src/Ably.PubSub.Server.NETFramework/packages.config
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="Microsoft.CodeQuality.Analyzers" version="2.9.6" targetFramework="net462" developmentDependency="true" />
+  <package id="StyleCop.Analyzers" version="1.1.118" targetFramework="net462" developmentDependency="true" />
+</packages>
diff --git a/src/Ably.PubSub.Server/Ably.PubSub.Server.csproj b/src/Ably.PubSub.Server/Ably.PubSub.Server.csproj
new file mode 100644
index 000000000..f1669d01a
--- /dev/null
+++ b/src/Ably.PubSub.Server/Ably.PubSub.Server.csproj
@@ -0,0 +1,60 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <!-- Identical to the core head, so every consumer of the core has a Server asset. -->
+    <TargetFrameworks>netstandard2.0;net6.0;net7.0</TargetFrameworks>
+    <CodeAnalysisRuleSet>..\IO.Ably.ruleset</CodeAnalysisRuleSet>
+    <Configurations>Debug;Release;package</Configurations>
+    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <AssemblyName>Ably.PubSub.Server</AssemblyName>
+    <RootNamespace>IO.Ably.PubSub.Server</RootNamespace>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(MSBuildRuntimeType)'=='Mono'">
+    <TargetFramework>netstandard2.0</TargetFramework>
+  </PropertyGroup>
+
+  <!-- Signed under package builds only, in lockstep with Ably.PubSub.Core: a consumer of the
+       signed core must never have to mix signed and unsigned Ably assemblies, and the plain
+       (non-Package) builds keep everything unsigned so the core's keyless
+       InternalsVisibleTo test access keeps compiling. -->
+  <PropertyGroup Condition="'$(Package)'=='True'">
+    <SignAssembly>true</SignAssembly>
+    <AssemblyOriginatorKeyFile>..\..\IO.Ably.snk</AssemblyOriginatorKeyFile>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='package|AnyCPU'">
+    <OutputPath>bin\package</OutputPath>
+  </PropertyGroup>
+
+  <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+
+  <PropertyGroup Condition=" '$(Configuration)' == 'Release' ">
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="..\CommonAssemblyInfo.cs" Link="Properties\CommonAssemblyInfo.cs" />
+    <!-- Shared source, compiled into both door assemblies rather than published. -->
+    <Compile Include="..\Ably.PubSub.Side\Side.cs" Link="Side.cs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <AdditionalFiles Include="..\stylecop.json" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="StyleCop.Analyzers" Version="1.1.118">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Ably.PubSub.Core\Ably.PubSub.Core.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/Ably.PubSub.Server/PubSubServer.cs b/src/Ably.PubSub.Server/PubSubServer.cs
new file mode 100644
index 000000000..beed7412b
--- /dev/null
+++ b/src/Ably.PubSub.Server/PubSubServer.cs
@@ -0,0 +1,103 @@
+using System;
+using IO.Ably.PubSub.Internal;
+
+namespace IO.Ably.PubSub.Server
+{
+    /// <summary>
+    /// Entry point for Ably Pub/Sub applications that run on a server - an ASP.NET or Azure host,
+    /// a worker, a console app or any other backend the end user does not hold.
+    /// <para>
+    /// These factory methods are the only supported way to create a client from this package.
+    /// The Ably.PubSub.Core package that carries the implementation is an internal dependency: a
+    /// client constructed directly from <see cref="AblyRealtime"/> or <see cref="AblyRest"/> is
+    /// not classified as server-side, which Ably's platform behaviour and billing depend on.
+    /// </para>
+    /// <para>
+    /// The returned clients are the ordinary <see cref="AblyRealtime"/> and
+    /// <see cref="AblyRest"/>, so the whole of the <c>IO.Ably</c> API remains available;
+    /// installing this package rather than Ably.PubSub.Device states where the code runs. What
+    /// the doors add is an agent entry declaring the server side, and per PDR-091 that entry is
+    /// what earns the monthly-active-user exemption on API-key authentication.
+    /// </para>
+    /// </summary>
+    public static class PubSubServer
+    {
+        /// <summary>
+        /// Creates a server-side realtime client from an API key or an Ably token.
+        /// </summary>
+        /// <param name="keyOrToken">
+        /// A valid Ably API key (of the form <c>APP_ID.KEY_ID:KEY_SECRET</c>) or an Ably token.
+        /// The core applies the same colon rule its own constructors use to tell them apart.
+        /// </param>
+        /// <returns> A connected-on-demand realtime client. </returns>
+        public static AblyRealtime CreateRealtimeClient(string keyOrToken)
+        {
+            return CreateRealtimeClient(new ClientOptions(keyOrToken));
+        }
+
+        /// <summary>
+        /// Creates a server-side realtime client from a set of client options.
+        /// </summary>
+        /// <param name="options"> The client options. </param>
+        /// <returns> A connected-on-demand realtime client. </returns>
+        /// <exception cref="ArgumentNullException"> Thrown when <paramref name="options"/> is null. </exception>
+        public static AblyRealtime CreateRealtimeClient(ClientOptions options)
+        {
+            // The core constructor is [Obsolete] to steer consumers to the doors; this door is
+            // the sanctioned caller, constructing the client from the side-stamped copy.
+#pragma warning disable CS0618
+            return new AblyRealtime(Side.WithSideAgent(options, Side.ServerAgentIdentifier));
+#pragma warning restore CS0618
+        }
+
+        /// <summary>
+        /// Creates a server-side realtime client, configured by the supplied action.
+        /// </summary>
+        /// <param name="configure"> Action that populates the client options. </param>
+        /// <returns> A connected-on-demand realtime client. </returns>
+        /// <exception cref="ArgumentNullException"> Thrown when <paramref name="configure"/> is null. </exception>
+        public static AblyRealtime CreateRealtimeClient(Action<ClientOptions> configure)
+        {
+            return CreateRealtimeClient(Side.Configure(configure));
+        }
+
+        /// <summary>
+        /// Creates a server-side HTTP (REST) client from an API key or an Ably token.
+        /// </summary>
+        /// <param name="keyOrToken">
+        /// A valid Ably API key (of the form <c>APP_ID.KEY_ID:KEY_SECRET</c>) or an Ably token.
+        /// The core applies the same colon rule its own constructors use to tell them apart.
+        /// </param>
+        /// <returns> An HTTP client. </returns>
+        public static AblyRest CreateHttpClient(string keyOrToken)
+        {
+            return CreateHttpClient(new ClientOptions(keyOrToken));
+        }
+
+        /// <summary>
+        /// Creates a server-side HTTP (REST) client from a set of client options.
+        /// </summary>
+        /// <param name="options"> The client options. </param>
+        /// <returns> An HTTP client. </returns>
+        /// <exception cref="ArgumentNullException"> Thrown when <paramref name="options"/> is null. </exception>
+        public static AblyRest CreateHttpClient(ClientOptions options)
+        {
+            // The core constructor is [Obsolete] to steer consumers to the doors; this door is
+            // the sanctioned caller, constructing the client from the side-stamped copy.
+#pragma warning disable CS0618
+            return new AblyRest(Side.WithSideAgent(options, Side.ServerAgentIdentifier));
+#pragma warning restore CS0618
+        }
+
+        /// <summary>
+        /// Creates a server-side HTTP (REST) client, configured by the supplied action.
+        /// </summary>
+        /// <param name="configure"> Action that populates the client options. </param>
+        /// <returns> An HTTP client. </returns>
+        /// <exception cref="ArgumentNullException"> Thrown when <paramref name="configure"/> is null. </exception>
+        public static AblyRest CreateHttpClient(Action<ClientOptions> configure)
+        {
+            return CreateHttpClient(Side.Configure(configure));
+        }
+    }
+}
diff --git a/src/Ably.PubSub.Shared/AblyRealtime.cs b/src/Ably.PubSub.Shared/AblyRealtime.cs
index 58ff6b9db..6bb85a440 100644
--- a/src/Ably.PubSub.Shared/AblyRealtime.cs
+++ b/src/Ably.PubSub.Shared/AblyRealtime.cs
@@ -38,6 +38,7 @@ public class AblyRealtime : IRealtimeClient, IDisposable
         /// client will be rejected once MAU-based pricing is live.
         /// </remarks>
         /// <param name="key">String key (obtained from application dashboard).</param>
+        [Obsolete("Construct via PubSubDevice.CreateClient or PubSubServer.CreateRealtimeClient; a directly-constructed client is unclassified and will be rejected once MAU-based pricing is live.", error: false)]
         public AblyRealtime(string key)
             : this(new ClientOptions(key))
         {
@@ -55,6 +56,7 @@ public AblyRealtime(string key)
         /// client will be rejected once MAU-based pricing is live.
         /// </remarks>
         /// <param name="options"><see cref="ClientOptions"/>.</param>
+        [Obsolete("Construct via PubSubDevice.CreateClient or PubSubServer.CreateRealtimeClient; a directly-constructed client is unclassified and will be rejected once MAU-based pricing is live.", error: false)]
         public AblyRealtime(ClientOptions options)
             : this(options, CreateRestFunc, IoC.MobileDevice)
         {
diff --git a/src/Ably.PubSub.Shared/AblyRest.cs b/src/Ably.PubSub.Shared/AblyRest.cs
index e36247a63..29d977a3a 100644
--- a/src/Ably.PubSub.Shared/AblyRest.cs
+++ b/src/Ably.PubSub.Shared/AblyRest.cs
@@ -29,6 +29,7 @@ public sealed class AblyRest : IRestClient
         /// client will be rejected once MAU-based pricing is live.
         /// </remarks>
         /// <param name="apiKey">Full api key.</param>
+        [Obsolete("Construct via PubSubServer.CreateHttpClient; a directly-constructed client is unclassified and will be rejected once MAU-based pricing is live.", error: false)]
         public AblyRest(string apiKey)
             : this(new ClientOptions(apiKey))
         {
@@ -52,6 +53,7 @@ public AblyRest(string apiKey)
         /// client will be rejected once MAU-based pricing is live.
         /// </remarks>
         /// <param name="init">Action delegate which receives a empty options object.</param>
+        [Obsolete("Construct via PubSubServer.CreateHttpClient; a directly-constructed client is unclassified and will be rejected once MAU-based pricing is live.", error: false)]
         public AblyRest(Action<ClientOptions> init)
         {
             Options = new ClientOptions();
@@ -70,6 +72,7 @@ public AblyRest(Action<ClientOptions> init)
         /// client will be rejected once MAU-based pricing is live.
         /// </remarks>
         /// <param name="clientOptions">instance of clientOptions.</param>
+        [Obsolete("Construct via PubSubServer.CreateHttpClient; a directly-constructed client is unclassified and will be rejected once MAU-based pricing is live.", error: false)]
         public AblyRest(ClientOptions clientOptions)
             : this(clientOptions, IoC.MobileDevice)
         {
diff --git a/src/Ably.PubSub.Shared/Agent.cs b/src/Ably.PubSub.Shared/Agent.cs
index 147e9c20a..166058cce 100644
--- a/src/Ably.PubSub.Shared/Agent.cs
+++ b/src/Ably.PubSub.Shared/Agent.cs
@@ -34,7 +34,19 @@ public static class OS
         }
 
         internal const string AblyAgentHeader = "Ably-Agent";
-        private static readonly string AblySdkIdentifier = $"ably-dotnet/{Defaults.LibraryVersion}"; // RSC7d1
+
+        // RSC7d1. The family identifier for this SDK.
+        //
+        // It flips from `ably-dotnet` to `ably-pubsub-dotnet` at the Pub/Sub package split
+        // (PDR-091b), and the flip is the point: the identifier alone then partitions legacy
+        // traffic (`ably-dotnet/*`, still emitted by the 1.x maintenance branch, which keeps
+        // the old identifier) from new-package traffic (`ably-pubsub-dotnet/*`), without
+        // needing to correlate versions. Registered in ably-common
+        // (https://github.com/ably/ably-common/pull/361) as a versioned `sdk` entry.
+        //
+        // The per-side flags (`ably-pubsub-device` / `ably-pubsub-server`) are stamped by the
+        // door packages, not here — see src/Ably.PubSub.Side/Side.cs.
+        private static readonly string AblySdkIdentifier = $"ably-pubsub-dotnet/{Defaults.LibraryVersion}";
 
         private static readonly Lazy<string> _dotnetRuntimeIdentifier =
             new Lazy<string>(() => GetDotnetRuntimeIdentifier());
diff --git a/src/Ably.PubSub.Shared/ClientOptions.cs b/src/Ably.PubSub.Shared/ClientOptions.cs
index b93a57e4f..6cd77993c 100644
--- a/src/Ably.PubSub.Shared/ClientOptions.cs
+++ b/src/Ably.PubSub.Shared/ClientOptions.cs
@@ -454,5 +454,93 @@ public ClientOptions(string key)
             : base(key)
         {
         }
+
+        /// <summary>
+        /// Creates a member-wise copy of these options. Value-typed members are copied by value;
+        /// the mutable dictionary members (<see cref="Agents"/>, <see cref="AuthOptions.AuthHeaders"/>,
+        /// <see cref="AuthOptions.AuthParams"/> and <see cref="TransportParams"/>) are copied into new
+        /// dictionaries so the copy can be mutated without affecting the original; every other
+        /// reference-typed member (delegates, <see cref="AuthOptions.TokenDetails"/>,
+        /// <see cref="LogHandler"/>, <see cref="HttpClient"/>, <see cref="TransportFactory"/>,
+        /// <see cref="CustomContext"/>, <see cref="DefaultTokenParams"/> and <see cref="ChannelDefaults"/>)
+        /// is shared by reference, matching how the core's own constructors retain them.
+        /// <para>
+        /// This is the copy the door packages (Ably.PubSub.Device / Ably.PubSub.Server) stamp their
+        /// side agent onto, so that stamping a client never mutates the caller's own options instance.
+        /// It lives here rather than in the door helper because <see cref="RestHost"/>,
+        /// <see cref="RealtimeHost"/> and <see cref="FallbackHosts"/> are write-only from outside the
+        /// class and can only be carried across from inside it.
+        /// </para>
+        /// </summary>
+        /// <returns>A copy of these options.</returns>
+        public ClientOptions Clone()
+        {
+            var copy = new ClientOptions
+            {
+                // AuthOptions members.
+                AuthCallback = AuthCallback,
+                AuthUrl = AuthUrl,
+                AuthMethod = AuthMethod,
+                Key = Key,
+                Token = Token,
+                TokenDetails = TokenDetails,
+                AuthHeaders = AuthHeaders == null ? null : new Dictionary<string, string>(AuthHeaders),
+                AuthParams = AuthParams == null ? null : new Dictionary<string, string>(AuthParams),
+                QueryTime = QueryTime,
+                UseTokenAuth = UseTokenAuth,
+
+                // ClientOptions members.
+                AutoConnect = AutoConnect,
+                ClientId = ClientId,
+                DefaultTokenParams = DefaultTokenParams,
+                QueueMessages = QueueMessages,
+                EchoMessages = EchoMessages,
+                Recover = Recover,
+                LogLevel = LogLevel,
+                LogHandler = LogHandler,
+                Port = Port,
+                Tls = Tls,
+                TlsPort = TlsPort,
+                UseBinaryProtocol = UseBinaryProtocol,
+                DisconnectedRetryTimeout = DisconnectedRetryTimeout,
+                SuspendedRetryTimeout = SuspendedRetryTimeout,
+                ChannelRetryTimeout = ChannelRetryTimeout,
+                HttpOpenTimeout = HttpOpenTimeout,
+                HttpRequestTimeout = HttpRequestTimeout,
+                FallbackRetryTimeout = FallbackRetryTimeout,
+                HttpMaxRetryCount = HttpMaxRetryCount,
+                HttpMaxRetryDuration = HttpMaxRetryDuration,
+                ChannelDefaults = ChannelDefaults,
+                Environment = Environment,
+                TransportFactory = TransportFactory,
+                IdempotentRestPublishing = IdempotentRestPublishing,
+                TransportParams = TransportParams == null ? null : new Dictionary<string, object>(TransportParams),
+                CustomContext = CustomContext,
+                AutomaticNetworkStateMonitoring = AutomaticNetworkStateMonitoring,
+                HeartbeatMonitorDelay = HeartbeatMonitorDelay,
+                AddRequestIds = AddRequestIds,
+                PushAdminFullWait = PushAdminFullWait,
+                Agents = Agents == null ? null : new Dictionary<string, string>(Agents),
+                HttpClient = HttpClient,
+
+                // Internal state the core reads.
+                Logger = Logger,
+                SkipInternetCheck = SkipInternetCheck,
+                RealtimeRequestTimeout = RealtimeRequestTimeout,
+            };
+
+            // Write-only / private-field members, only reachable from inside the class.
+            copy._restHost = _restHost;
+            copy._realtimeHost = _realtimeHost;
+            copy._fallbackHosts = _fallbackHosts;
+            copy._nowFunc = _nowFunc;
+
+#pragma warning disable 618
+            copy.FallbackHostsUseDefault = FallbackHostsUseDefault;
+            copy.CaptureCurrentSynchronizationContext = CaptureCurrentSynchronizationContext;
+#pragma warning restore 618
+
+            return copy;
+        }
     }
 }
diff --git a/src/Ably.PubSub.Side/Side.cs b/src/Ably.PubSub.Side/Side.cs
new file mode 100644
index 000000000..d55de5fed
--- /dev/null
+++ b/src/Ably.PubSub.Side/Side.cs
@@ -0,0 +1,121 @@
+using System;
+using System.Collections.Generic;
+
+namespace IO.Ably.PubSub.Internal
+{
+    /// <summary>
+    /// Private helper shared by Ably.PubSub.Device and Ably.PubSub.Server. It is compiled into
+    /// each door assembly by a <c>&lt;Compile Include&gt;</c> item rather than published, so the two
+    /// packages can share this code without a third NuGet package existing for it to live in.
+    /// This is the .NET analogue of ably-js's <c>packages/shared/side.ts</c> and ably-java's
+    /// <c>shared/.../Side.java</c>.
+    /// <para>
+    /// PDR-091 keeps Ably.PubSub.Core itself as the shared core, so nothing here may grow into a
+    /// general abstraction over the core: it exists only to stamp the side a package declares.
+    /// </para>
+    /// </summary>
+    internal static class Side
+    {
+        // The `-device` / `-server` suffix on both identifiers below is load-bearing, not
+        // cosmetic. On API-key auth the realtime system grants the MAU server exemption by
+        // matching an agent entry ending in `-server`, and an identifier that is not yet in the
+        // ably-common registry is classified by that suffix alone. Renaming either without
+        // preserving its suffix silently reclassifies every client the package constructs.
+        //
+        // Both live here rather than in the package that uses each, so the naming scheme can be
+        // changed in one place.
+
+        /// <summary>
+        /// The agent identifier declaring the device side, sent by Ably.PubSub.Device.
+        /// </summary>
+        internal const string DeviceAgentIdentifier = "ably-pubsub-device";
+
+        /// <summary>
+        /// The agent identifier declaring the server side, sent by Ably.PubSub.Server.
+        /// <para>
+        /// This is the entry that earns the MAU exemption on API-key auth, so its <c>-server</c>
+        /// suffix is the one with billing consequences.
+        /// </para>
+        /// </summary>
+        internal const string ServerAgentIdentifier = "ably-pubsub-server";
+
+        /// <summary>
+        /// Returns a copy of the caller's options carrying the agent entry that declares this
+        /// package's side.
+        /// <para>
+        /// The core stores the options object it is given <b>by reference</b>, so stamping the
+        /// side onto the caller's own instance would leak the flag into any other client built
+        /// from the same options — both doors reused on one options object, or a plain
+        /// <c>new AblyRealtime(options)</c>. To prevent that, the options are copied via
+        /// <see cref="ClientOptions.Clone()"/> and the side is stamped onto the copy; the caller's
+        /// instance and its <c>Agents</c> dictionary are left untouched. The copy lives in the core
+        /// (not here) because <c>RestHost</c>/<c>RealtimeHost</c>/<c>FallbackHosts</c> are
+        /// write-only from outside the class and cannot be carried across by a copy located here.
+        /// </para>
+        /// <para>
+        /// The caller's <c>Agents</c> entries are preserved alongside the side stamp, so an SDK
+        /// layered on top of this package keeps its attribution. The side stamp is applied last
+        /// and so wins a collision on its own identifier: which side the package declares is the
+        /// package's to state, not the caller's to redefine.
+        /// </para>
+        /// <para>
+        /// The stamp is deliberately <b>versionless</b> — a bare <c>ably-pubsub-server</c> token
+        /// rather than <c>ably-pubsub-server/2.0.0</c>. A version on the flag would say
+        /// version-of-what: the flag is a cross-SDK statement about where the code runs, the
+        /// door package is released in lockstep with the core, whose version the family
+        /// identifier (<c>ably-pubsub-dotnet/&lt;version&gt;</c>) already carries, and the
+        /// ably-common registry models the flags like <c>browser</c>, with
+        /// <c>versioned: false</c>. See ably-js#2297. <c>Agent.AddAgentIdentifier</c> in the core
+        /// already emits a bare token for a null or empty version, so a null value here is all
+        /// that is needed.
+        /// </para>
+        /// </summary>
+        /// <param name="options"> The options the caller passed to the door. </param>
+        /// <param name="identifier"> The side-declaring agent identifier to stamp. </param>
+        /// <returns> A copy of the options, with the side stamped into its <c>Agents</c> dictionary. </returns>
+        /// <exception cref="ArgumentNullException"> Thrown when <paramref name="options"/> is null. </exception>
+        internal static ClientOptions WithSideAgent(ClientOptions options, string identifier)
+        {
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+
+            // Copy before stamping: the core keeps the options object by reference, so mutating the
+            // caller's instance would let this side flag leak into another client built from the
+            // same options. Clone() already gives Agents its own dictionary.
+            var copy = options.Clone();
+
+            if (copy.Agents == null)
+            {
+                copy.Agents = new Dictionary<string, string>();
+            }
+
+            // Applied last, so the side wins a collision on its own key. Null value => bare
+            // token, per the versionless-flag reasoning above.
+            copy.Agents[identifier] = null;
+
+            return copy;
+        }
+
+        /// <summary>
+        /// Builds a fresh <see cref="ClientOptions"/> configured by the supplied action. The core
+        /// clients have no such constructor overload, so the doors provide one uniformly.
+        /// </summary>
+        /// <param name="configure"> Action that populates the new options. </param>
+        /// <returns> The populated options. </returns>
+        /// <exception cref="ArgumentNullException"> Thrown when <paramref name="configure"/> is null. </exception>
+        internal static ClientOptions Configure(Action<ClientOptions> configure)
+        {
+            if (configure == null)
+            {
+                throw new ArgumentNullException(nameof(configure));
+            }
+
+            var options = new ClientOptions();
+            configure(options);
+
+            return options;
+        }
+    }
+}
diff --git a/src/Ably.PubSub.Tests.DotNET/Ably.PubSub.Tests.DotNET.csproj b/src/Ably.PubSub.Tests.DotNET/Ably.PubSub.Tests.DotNET.csproj
index 87c98ee2f..3bb109682 100644
--- a/src/Ably.PubSub.Tests.DotNET/Ably.PubSub.Tests.DotNET.csproj
+++ b/src/Ably.PubSub.Tests.DotNET/Ably.PubSub.Tests.DotNET.csproj
@@ -4,10 +4,12 @@
     <TargetFrameworks>net6.0;net7.0</TargetFrameworks>
     <CodeAnalysisRuleSet>..\IO.Ably.Tests.ruleset</CodeAnalysisRuleSet>
     <LangVersion>8</LangVersion>
+    <!-- 618: the tests deliberately exercise the [Obsolete] core constructors (unclassified-client coverage). -->
+    <NoWarn>$(NoWarn);618</NoWarn>
   </PropertyGroup>
 
 	<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
-    <NoWarn>1701;1702;SA0001;NU1701</NoWarn>
+    <NoWarn>1701;1702;SA0001;NU1701;618</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>
@@ -48,6 +50,11 @@
 
   <ItemGroup>
     <ProjectReference Include="..\Ably.PubSub.Core\Ably.PubSub.Core.csproj" />
+    <!-- The door specs live in this head rather than Ably.PubSub.Tests.Shared because
+         Ably.PubSub.Device has no net462 asset (plan decision 5b), so the shared project
+         cannot reference it from the .NET Framework test head. -->
+    <ProjectReference Include="..\Ably.PubSub.Device\Ably.PubSub.Device.csproj" />
+    <ProjectReference Include="..\Ably.PubSub.Server\Ably.PubSub.Server.csproj" />
   </ItemGroup>
 
   <ItemGroup>  	
diff --git a/src/Ably.PubSub.Tests.DotNET/PubSub/PubSubDoorSandboxSpecs.cs b/src/Ably.PubSub.Tests.DotNET/PubSub/PubSubDoorSandboxSpecs.cs
new file mode 100644
index 000000000..2caf992ac
--- /dev/null
+++ b/src/Ably.PubSub.Tests.DotNET/PubSub/PubSubDoorSandboxSpecs.cs
@@ -0,0 +1,85 @@
+using System;
+using System.Threading.Tasks;
+using FluentAssertions;
+using IO.Ably.PubSub.Device;
+using IO.Ably.PubSub.Server;
+using IO.Ably.Realtime;
+using IO.Ably.Tests;
+using IO.Ably.Tests.Infrastructure;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace IO.Ably.Tests.PubSub
+{
+    /// <summary>
+    /// Dual-construction-mode conformance: a client built through each door must actually work
+    /// against the Ably sandbox, not just carry the right agent over the fake transport. One
+    /// realtime publish/subscribe round-trip per realtime door, and one REST call for the HTTP
+    /// door. Tagged type=integration so it runs in the existing Test.NetStandard.Integration legs.
+    /// </summary>
+    [Collection("SandBox Connection")]
+    [Trait("type", "integration")]
+    public class PubSubDoorSandboxSpecs : SandboxSpecs
+    {
+        public PubSubDoorSandboxSpecs(AblySandboxFixture fixture, ITestOutputHelper output)
+            : base(fixture, output)
+        {
+        }
+
+        [Fact]
+        [Trait("spec", "RSC7d")]
+        public async Task ServerRealtimeDoor_ConnectsAndRoundTripsAMessage()
+        {
+            var client = PubSubServer.CreateRealtimeClient(await DoorOptions());
+
+            await RoundTripAMessage(client);
+        }
+
+        [Fact]
+        [Trait("spec", "RSC7d")]
+        public async Task DeviceDoor_ConnectsAndRoundTripsAMessage()
+        {
+            var client = PubSubDevice.CreateClient(await DoorOptions());
+
+            await RoundTripAMessage(client);
+        }
+
+        [Fact]
+        [Trait("spec", "RSC7d")]
+        public async Task ServerHttpDoor_CompletesARestCall()
+        {
+            var client = PubSubServer.CreateHttpClient(await DoorOptions());
+
+            var serverTime = await client.TimeAsync();
+
+            serverTime.Should().BeCloseTo(DateTimeOffset.UtcNow, TimeSpan.FromMinutes(15));
+        }
+
+        private static async Task<ClientOptions> DoorOptions()
+        {
+            var settings = await AblySandboxFixture.GetSettings();
+            var options = settings.CreateDefaultOptions();
+            options.TransportFactory = new TestTransportFactory();
+            return options;
+        }
+
+        private async Task RoundTripAMessage(AblyRealtime client)
+        {
+            using (client)
+            {
+                await client.WaitForState(ConnectionState.Connected);
+
+                var channel = client.Channels.Get("pubsub-door-smoke".AddRandomSuffix());
+                Message received = null;
+                channel.Subscribe(message => received = message);
+                await channel.AttachAsync();
+
+                var result = await channel.PublishAsync(new Message("greeting", "hello"));
+                result.IsSuccess.Should().BeTrue();
+
+                await new ConditionalAwaiter(() => received != null);
+                received.Data.Should().Be("hello");
+            }
+        }
+    }
+}
diff --git a/src/Ably.PubSub.Tests.DotNET/PubSub/PubSubPackageSpecs.cs b/src/Ably.PubSub.Tests.DotNET/PubSub/PubSubPackageSpecs.cs
new file mode 100644
index 000000000..983d649a1
--- /dev/null
+++ b/src/Ably.PubSub.Tests.DotNET/PubSub/PubSubPackageSpecs.cs
@@ -0,0 +1,414 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net;
+using System.Net.Http;
+using System.Threading.Tasks;
+using FluentAssertions;
+using IO.Ably.PubSub.Device;
+using IO.Ably.PubSub.Server;
+using IO.Ably.Tests;
+using IO.Ably.Tests.Infrastructure;
+using IO.Ably.Tests.Realtime;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace IO.Ably.Tests.PubSub
+{
+    /// <summary>
+    /// The agent contract of the two door packages. These assertions are what Ably's billing
+    /// reads: the realtime system grants the MAU server exemption on API-key auth by matching an
+    /// agent entry ending in `-server`, so a rename, a stray version suffix or a lost stamp must
+    /// fail here loudly rather than surface as a billing discrepancy.
+    ///
+    /// The identifiers are written out as literals on purpose - asserting against
+    /// `Side.ServerAgentIdentifier` would make a rename of the constant pass silently.
+    ///
+    /// Every spec either disables AutoConnect or supplies the fake transport factory, so no unit
+    /// test here opens a network connection. The one gap that follows from that is noted on
+    /// StringOverloadSpecs below.
+    /// </summary>
+    [Trait("spec", "RSC7d")]
+    public class PubSubPackageSpecs : AblySpecs
+    {
+        private const string DeviceFlag = "ably-pubsub-device";
+        private const string ServerFlag = "ably-pubsub-server";
+        private const string FamilyPrefix = "ably-pubsub-dotnet/";
+
+        public PubSubPackageSpecs(ITestOutputHelper output)
+            : base(output)
+        {
+        }
+
+        private static string FamilyIdentifier => FamilyPrefix + Defaults.LibraryVersion;
+
+        [Fact]
+        public async Task ServerHttpClient_SendsBareServerFlagAndFamilyIdentifier()
+        {
+            var agentValues = await CaptureHttpAgentTokens(
+                handler => PubSubServer.CreateHttpClient(options => UseFakeHttp(options, handler)));
+
+            AssertServerSide(agentValues);
+        }
+
+        [Fact]
+        public async Task ServerRealtimeClient_SendsBareServerFlagAndFamilyIdentifier()
+        {
+            var agentValues = await CaptureRealtimeAgentTokens(
+                factory => PubSubServer.CreateRealtimeClient(o => UseFakeTransport(o, factory)));
+
+            AssertServerSide(agentValues);
+        }
+
+        [Fact]
+        public async Task DeviceClient_SendsBareDeviceFlagOverHttp()
+        {
+            var agentValues = await CaptureHttpAgentTokens(
+                handler => PubSubDevice.CreateClient(options => UseFakeHttp(options, handler)).RestClient);
+
+            AssertDeviceSide(agentValues);
+        }
+
+        [Fact]
+        public async Task DeviceClient_SendsBareDeviceFlagOnTheRealtimeConnection()
+        {
+            var agentValues = await CaptureRealtimeAgentTokens(
+                factory => PubSubDevice.CreateClient(o => UseFakeTransport(o, factory)));
+
+            AssertDeviceSide(agentValues);
+        }
+
+        [Fact]
+        public async Task CoreConstructedRestClient_SendsNeitherSideFlag()
+        {
+            var agentValues = await CaptureHttpAgentTokens(handler =>
+            {
+                var options = new ClientOptions();
+                UseFakeHttp(options, handler);
+                return new AblyRest(options);
+            });
+
+            AssertNoSideFlag(agentValues);
+        }
+
+        [Fact]
+        public async Task CoreConstructedRealtimeClient_SendsNeitherSideFlagOnTheConnection()
+        {
+            var agentValues = await CaptureRealtimeAgentTokens(factory =>
+            {
+                var options = new ClientOptions();
+                UseFakeTransport(options, factory);
+                return new AblyRealtime(options);
+            });
+
+            AssertNoSideFlag(agentValues);
+        }
+
+        [Fact]
+        public async Task CallerSuppliedAgents_ArePreservedAlongsideTheFlag()
+        {
+            var agentValues = await CaptureHttpAgentTokens(handler =>
+                PubSubServer.CreateHttpClient(options =>
+                {
+                    UseFakeHttp(options, handler);
+                    options.Agents = new Dictionary<string, string> { { "chat-dotnet", "1.0.0" } };
+                }));
+
+            agentValues.Should().Contain("chat-dotnet/1.0.0");
+            AssertServerSide(agentValues);
+        }
+
+        [Fact]
+        public async Task CallerEntryUnderTheSidesOwnKey_IsOverriddenWithTheBareFlag()
+        {
+            // Which side the package declares is the package's to state, not the caller's to
+            // redefine, so the stamp is applied last and wins.
+            var agentValues = await CaptureHttpAgentTokens(handler =>
+                PubSubServer.CreateHttpClient(options =>
+                {
+                    UseFakeHttp(options, handler);
+                    options.Agents = new Dictionary<string, string> { { ServerFlag, "9.9.9" } };
+                }));
+
+            AssertServerSide(agentValues);
+        }
+
+        [Fact]
+        public void ServerHttpClient_WithNeitherKeyNorToken_FailsExactlyLikeTheCore()
+        {
+            // Deliberately no key, token, authUrl or authCallback.
+            Action viaDoor = () => PubSubServer.CreateHttpClient(options => { });
+            Action viaCore = () => _ = new AblyRest(new ClientOptions());
+
+            // The door neither requires nor injects auth: with no credentials it fails
+            // with exactly the core's own 40106 (and had it injected any credential,
+            // it would not throw at all).
+            var doorError = viaDoor.Should().Throw<AblyException>().Which.ErrorInfo;
+            var coreError = viaCore.Should().Throw<AblyException>().Which.ErrorInfo;
+
+            doorError.Code.Should().Be(40106);
+            coreError.Code.Should().Be(40106);
+            doorError.Message.Should().Be(coreError.Message);
+        }
+
+        [Fact]
+        public void CallersOwnOptionsInstance_IsNotMutated()
+        {
+            var callerAgents = new Dictionary<string, string> { { "chat-dotnet", "1.0.0" } };
+            var options = new ClientOptions(ValidKey) { AutoConnect = false, Agents = callerAgents };
+
+            using (PubSubServer.CreateRealtimeClient(options))
+            {
+                // The caller's dictionary instance is untouched.
+                callerAgents.Should().HaveCount(1);
+                callerAgents.Should().NotContainKey(ServerFlag);
+                callerAgents.Should().ContainKey("chat-dotnet");
+
+                // The caller's options instance is untouched: the door stamps a copy, so the
+                // original still points at the caller's own dictionary and carries no side flag.
+                options.Agents.Should().BeSameAs(callerAgents);
+                options.Agents.Should().NotContainKey(ServerFlag);
+            }
+        }
+
+        [Fact]
+        public void ReusingOneOptionsInstanceAcrossDoors_DoesNotAccumulateOrLeakSideFlags()
+        {
+            var options = new ClientOptions(ValidKey) { AutoConnect = false, SkipInternetCheck = true };
+
+            using (var server = PubSubServer.CreateRealtimeClient(options))
+            using (var device = PubSubDevice.CreateClient(options))
+            {
+                // Each client consumes its own stamped copy, never the caller's instance.
+                server.Options.Should().NotBeSameAs(options);
+                device.Options.Should().NotBeSameAs(options);
+
+                server.Options.Agents.Should().ContainKey(ServerFlag);
+                server.Options.Agents.Should().NotContainKey(DeviceFlag);
+
+                device.Options.Agents.Should().ContainKey(DeviceFlag);
+                device.Options.Agents.Should().NotContainKey(ServerFlag);
+
+                // The caller's own options carries neither flag - no cross-contamination.
+                options.Agents.Should().BeNull();
+            }
+        }
+
+        [Fact]
+        public void EveryDoor_RejectsNullOptions()
+        {
+            Assert.Throws<ArgumentNullException>(() => PubSubServer.CreateRealtimeClient((ClientOptions)null));
+            Assert.Throws<ArgumentNullException>(() => PubSubServer.CreateHttpClient((ClientOptions)null));
+            Assert.Throws<ArgumentNullException>(() => PubSubDevice.CreateClient((ClientOptions)null));
+        }
+
+        [Fact]
+        public void EveryDoor_RejectsANullConfigureAction()
+        {
+            Assert.Throws<ArgumentNullException>(() => PubSubServer.CreateRealtimeClient((Action<ClientOptions>)null));
+            Assert.Throws<ArgumentNullException>(() => PubSubServer.CreateHttpClient((Action<ClientOptions>)null));
+            Assert.Throws<ArgumentNullException>(() => PubSubDevice.CreateClient((Action<ClientOptions>)null));
+        }
+
+        [Fact]
+        public void OptionsOverloads_ReturnTheConcreteCoreTypes()
+        {
+            using (var realtime = PubSubServer.CreateRealtimeClient(NoConnectOptions()))
+            {
+                realtime.Should().BeOfType<AblyRealtime>();
+            }
+
+            PubSubServer.CreateHttpClient(NoConnectOptions()).Should().BeOfType<AblyRest>();
+
+            using (var device = PubSubDevice.CreateClient(NoConnectOptions()))
+            {
+                device.Should().BeOfType<AblyRealtime>();
+            }
+        }
+
+        [Fact]
+        public void ActionOverloads_ReturnTheConcreteCoreTypes()
+        {
+            using (var realtime = PubSubServer.CreateRealtimeClient(o => NoConnect(o)))
+            {
+                realtime.Should().BeOfType<AblyRealtime>();
+            }
+
+            PubSubServer.CreateHttpClient(o => NoConnect(o)).Should().BeOfType<AblyRest>();
+
+            using (var device = PubSubDevice.CreateClient(o => NoConnect(o)))
+            {
+                device.Should().BeOfType<AblyRealtime>();
+            }
+        }
+
+        /// <summary>
+        /// The string overload of every door hands the string to `new ClientOptions(keyOrToken)`,
+        /// which applies the core's own colon rule (AuthOptions: an Ably API key is
+        /// `APP_ID.KEY_ID:KEY_SECRET` and always contains a colon; a token never does), and then
+        /// takes the same stamping path as the options overload.
+        ///
+        /// Only the HTTP door is exercised here. `CreateRealtimeClient(string)` and
+        /// `CreateClient(string)` cannot set AutoConnect, so constructing one in a unit test
+        /// would open a real websocket - the flakiness noted on the superseded PR #1330. They
+        /// share this exact code path, and the realtime stamping itself is covered above through
+        /// the action overload with a fake transport.
+        /// </summary>
+        public class StringOverloadSpecs
+        {
+            [Fact]
+            public void AKeyLikeString_IsTreatedAsAnApiKeyAndStillStamped()
+            {
+                var client = PubSubServer.CreateHttpClient("appId.keyId:secret");
+
+                client.Options.Key.Should().Be("appId.keyId:secret");
+                client.Options.Token.Should().BeNullOrEmpty();
+                client.Options.Agents.Should().ContainKey(ServerFlag);
+                client.Options.Agents[ServerFlag].Should().BeNullOrEmpty();
+            }
+
+            [Fact]
+            public void ATokenLikeString_IsTreatedAsATokenAndStillStamped()
+            {
+                var client = PubSubServer.CreateHttpClient("a_token_with_no_colon");
+
+                client.Options.Token.Should().Be("a_token_with_no_colon");
+                client.Options.Key.Should().BeNullOrEmpty();
+                client.Options.Agents.Should().ContainKey(ServerFlag);
+                client.Options.Agents[ServerFlag].Should().BeNullOrEmpty();
+            }
+        }
+
+        private static ClientOptions NoConnectOptions()
+        {
+            var options = new ClientOptions(ValidKey);
+            NoConnect(options);
+            return options;
+        }
+
+        private static void NoConnect(ClientOptions options)
+        {
+            options.Key = ValidKey;
+            options.AutoConnect = false;
+            options.SkipInternetCheck = true;
+        }
+
+        private static void UseFakeHttp(ClientOptions options, FakeHttpMessageHandler handler)
+        {
+            NoConnect(options);
+            options.UseBinaryProtocol = false;
+            options.HttpClient = new HttpClient(handler);
+        }
+
+        private static void UseFakeTransport(ClientOptions options, FakeTransportFactory factory)
+        {
+            options.Key = ValidKey;
+            options.SkipInternetCheck = true;
+            options.TransportFactory = factory;
+        }
+
+        /// <summary>
+        /// Drives a real request through the door-created REST client and returns the
+        /// `Ably-Agent` header the core actually put on the wire, split into tokens.
+        /// </summary>
+        private static async Task<string[]> CaptureHttpAgentTokens(Func<FakeHttpMessageHandler, AblyRest> createClient)
+        {
+            var response = new HttpResponseMessage(HttpStatusCode.OK)
+            {
+                Content = new StringContent("[1500000000000]"),
+            };
+            response.Content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
+
+            var handler = new FakeHttpMessageHandler(response);
+            var client = createClient(handler);
+
+            await client.TimeAsync();
+
+            handler.LastRequest.Should().NotBeNull();
+            var values = handler.LastRequest.Headers.GetValues(Agent.AblyAgentHeader).ToArray();
+            values.Should().HaveCount(1);
+
+            return values[0].Split(' ');
+        }
+
+        /// <summary>
+        /// Constructs a door-created realtime client over the fake transport and returns the
+        /// agent tokens from the connection query parameters.
+        ///
+        /// Note the query key: `TransportParams.GetParams()` sends the agent under
+        /// `Ably-Agent`, while spec RTN2g names the parameter `agent`. Whether that is a latent
+        /// bug is a separate question (plan step 14); this spec asserts on whatever key the core
+        /// currently uses so it does not pre-empt the answer.
+        /// </summary>
+        private static async Task<string[]> CaptureRealtimeAgentTokens(Func<FakeTransportFactory, AblyRealtime> createClient)
+        {
+            var factory = new FakeTransportFactory();
+            using (createClient(factory))
+            {
+                // The connection is established off the calling thread, so wait for the factory
+                // to be asked for a transport rather than assuming it already has been.
+                using (var awaiter = new ConditionalAwaiter(
+                    () => factory.LastCreatedTransport != null,
+                    () => "the fake transport factory was never asked for a transport"))
+                {
+                    await awaiter;
+                }
+
+                var transport = factory.LastCreatedTransport;
+                transport.Should().NotBeNull("the fake transport factory should have been used instead of a real websocket");
+
+                var parameters = transport.Parameters.GetParams();
+                parameters.Should().ContainKey(Agent.AblyAgentHeader);
+
+                return parameters[Agent.AblyAgentHeader].Split(' ');
+            }
+        }
+
+        private static void AssertServicedByThisSdk(string[] agentValues)
+        {
+            agentValues.Should().Contain(
+                FamilyIdentifier,
+                $"the family identifier must be the versioned '{FamilyPrefix}<version>' token registered in ably-common");
+        }
+
+        private static void AssertServerSide(string[] agentValues)
+        {
+            AssertServicedByThisSdk(agentValues);
+
+            agentValues.Should().Contain(
+                ServerFlag,
+                "the server flag must be a bare token - the '-server' suffix is what earns the MAU exemption on API-key auth");
+            agentValues.Should().NotContain(
+                t => t.StartsWith(ServerFlag + "/", StringComparison.Ordinal),
+                "the side flag is deliberately versionless (ably-common models it with versioned: false)");
+            agentValues.Should().NotContain(
+                t => t.StartsWith(DeviceFlag, StringComparison.Ordinal),
+                "a server client must never declare the device side");
+        }
+
+        private static void AssertDeviceSide(string[] agentValues)
+        {
+            AssertServicedByThisSdk(agentValues);
+
+            agentValues.Should().Contain(DeviceFlag, "the device flag must be a bare token");
+            agentValues.Should().NotContain(
+                t => t.StartsWith(DeviceFlag + "/", StringComparison.Ordinal),
+                "the side flag is deliberately versionless (ably-common models it with versioned: false)");
+            agentValues.Should().NotContain(
+                t => t.StartsWith(ServerFlag, StringComparison.Ordinal),
+                "a device client must never declare the server side, which would earn it the MAU exemption");
+        }
+
+        private static void AssertNoSideFlag(string[] agentValues)
+        {
+            AssertServicedByThisSdk(agentValues);
+
+            agentValues.Should().NotContain(
+                t => t.StartsWith(ServerFlag, StringComparison.Ordinal),
+                "a client built directly from the core is unclassified and must never declare the server side");
+            agentValues.Should().NotContain(
+                t => t.StartsWith(DeviceFlag, StringComparison.Ordinal),
+                "a client built directly from the core is unclassified and must never declare the device side");
+        }
+    }
+}
diff --git a/src/Ably.PubSub.Tests.NETFramework/Ably.PubSub.Tests.NETFramework.csproj b/src/Ably.PubSub.Tests.NETFramework/Ably.PubSub.Tests.NETFramework.csproj
index 2c0588464..d27cf6312 100644
--- a/src/Ably.PubSub.Tests.NETFramework/Ably.PubSub.Tests.NETFramework.csproj
+++ b/src/Ably.PubSub.Tests.NETFramework/Ably.PubSub.Tests.NETFramework.csproj
@@ -13,6 +13,8 @@
     <FileAlignment>512</FileAlignment>
     <LangVersion>8</LangVersion>
     <TargetFrameworkProfile />
+    <!-- 618: the tests deliberately exercise the [Obsolete] core constructors (unclassified-client coverage). -->
+    <NoWarn>$(NoWarn);618</NoWarn>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>
diff --git a/src/Ably.PubSub.Tests.Shared/Realtime/ConnectionSpecs/ConnectionParameterSpecs.cs b/src/Ably.PubSub.Tests.Shared/Realtime/ConnectionSpecs/ConnectionParameterSpecs.cs
index 740708b2a..54d265f88 100644
--- a/src/Ably.PubSub.Tests.Shared/Realtime/ConnectionSpecs/ConnectionParameterSpecs.cs
+++ b/src/Ably.PubSub.Tests.Shared/Realtime/ConnectionSpecs/ConnectionParameterSpecs.cs
@@ -129,7 +129,7 @@ public async Task ShouldSetTransportAblyAgentHeader()
             var agentValues = LastCreatedTransport.Parameters.GetParams()[Agent.AblyAgentHeader].Split(' ');
             var keys = new List<string>()
             {
-                "ably-dotnet/",
+                "ably-pubsub-dotnet/",
                 Agent.DotnetRuntimeIdentifier,
                 Agent.OsIdentifier
             };
@@ -160,7 +160,7 @@ public async Task ShouldSetTransportCustomAblyAgentHeader()
             var agentValues = LastCreatedTransport.Parameters.GetParams()[Agent.AblyAgentHeader].Split(' ');
             var keys = new List<string>()
             {
-                "ably-dotnet/",
+                "ably-pubsub-dotnet/",
                 Agent.DotnetRuntimeIdentifier,
                 Agent.OsIdentifier,
                 "agent1",
diff --git a/src/Ably.PubSub.Tests.Shared/Rest/AblyHttpClientSpecs.cs b/src/Ably.PubSub.Tests.Shared/Rest/AblyHttpClientSpecs.cs
index a611be51a..45bb32e32 100644
--- a/src/Ably.PubSub.Tests.Shared/Rest/AblyHttpClientSpecs.cs
+++ b/src/Ably.PubSub.Tests.Shared/Rest/AblyHttpClientSpecs.cs
@@ -98,7 +98,7 @@ public async Task WhenCallingUrl_AddsDefaultAblyAgentHeader()
 
             var keys = new List<string>()
             {
-                "ably-dotnet/",
+                "ably-pubsub-dotnet/",
                 Agent.DotnetRuntimeIdentifier,
                 Agent.OsIdentifier
             };
@@ -140,7 +140,7 @@ public async Task WhenCallingUrl_AddsCustomizedAblyAgentHeader()
 
             var keys = new List<string>()
             {
-                "ably-dotnet/",
+                "ably-pubsub-dotnet/",
                 Agent.DotnetRuntimeIdentifier,
                 Agent.OsIdentifier,
                 "agent1",
diff --git a/src/Ably.PubSub.sln b/src/Ably.PubSub.sln
index bd85e51bc..c27a93ad4 100644
--- a/src/Ably.PubSub.sln
+++ b/src/Ably.PubSub.sln
@@ -33,6 +33,12 @@ Project("{D954291E-2A0B-460D-934E-DC6B0785DB48}") = "Ably.PubSub.Tests.Shared",
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "IO.Ably.DeltaCodec", "..\lib\delta-codec\IO.Ably.DeltaCodec\IO.Ably.DeltaCodec.csproj", "{412DEB5F-7936-4027-8BF8-977F23D465ED}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ably.PubSub.Device", "Ably.PubSub.Device\Ably.PubSub.Device.csproj", "{91E8141C-38F6-4CB2-A241-BDC34C470F73}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ably.PubSub.Server", "Ably.PubSub.Server\Ably.PubSub.Server.csproj", "{A92FE34C-1D98-4254-BE8C-BC403B053DB9}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ably.PubSub.Server.NETFramework", "Ably.PubSub.Server.NETFramework\Ably.PubSub.Server.NETFramework.csproj", "{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -125,6 +131,54 @@ Global
 		{412DEB5F-7936-4027-8BF8-977F23D465ED}.Release|x64.Build.0 = Release|Any CPU
 		{412DEB5F-7936-4027-8BF8-977F23D465ED}.Release|x86.ActiveCfg = Release|Any CPU
 		{412DEB5F-7936-4027-8BF8-977F23D465ED}.Release|x86.Build.0 = Release|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Debug|ARM.ActiveCfg = Debug|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Debug|ARM.Build.0 = Debug|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Debug|x64.Build.0 = Debug|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Debug|x86.Build.0 = Debug|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Release|Any CPU.Build.0 = Release|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Release|ARM.ActiveCfg = Release|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Release|ARM.Build.0 = Release|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Release|x64.ActiveCfg = Release|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Release|x64.Build.0 = Release|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Release|x86.ActiveCfg = Release|Any CPU
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73}.Release|x86.Build.0 = Release|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Debug|ARM.ActiveCfg = Debug|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Debug|ARM.Build.0 = Debug|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Debug|x64.Build.0 = Debug|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Debug|x86.Build.0 = Debug|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Release|ARM.ActiveCfg = Release|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Release|ARM.Build.0 = Release|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Release|x64.ActiveCfg = Release|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Release|x64.Build.0 = Release|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Release|x86.ActiveCfg = Release|Any CPU
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9}.Release|x86.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|ARM.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|ARM.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x64.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Debug|x86.Build.0 = Debug|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|Any CPU.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|ARM.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|ARM.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x64.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x64.Build.0 = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x86.ActiveCfg = Release|Any CPU
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -138,6 +192,9 @@ Global
 		{4805A9DA-3412-4BE8-8B95-5A0EFDA1AC01} = {C2F43DB7-AAA0-4687-9897-5D686EC91245}
 		{1609F12C-8216-4E7C-ADE0-240BFE160242} = {C2F43DB7-AAA0-4687-9897-5D686EC91245}
 		{412DEB5F-7936-4027-8BF8-977F23D465ED} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
+		{91E8141C-38F6-4CB2-A241-BDC34C470F73} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
+		{A92FE34C-1D98-4254-BE8C-BC403B053DB9} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
+		{7B3C1F42-9D5E-4A87-B1C6-2E4F8A9D0B31} = {8A0F718E-2168-4CC7-8F7B-A65508B52B0F}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {F69D4156-FC22-4B8E-AD72-2A7323D42CC4}
diff --git a/src/IO.Ably.ruleset b/src/IO.Ably.ruleset
index aecc9528f..6b64cdad3 100644
--- a/src/IO.Ably.ruleset
+++ b/src/IO.Ably.ruleset
@@ -212,7 +212,6 @@
     <Rule Id="CS7090" Action="None" />
     <Rule Id="CS7095" Action="None" />
     <Rule Id="CS8001" Action="None" />
-    <Rule Id="CS8002" Action="None" />
     <Rule Id="CS8009" Action="None" />
     <Rule Id="CS8012" Action="None" />
     <Rule Id="CS8018" Action="None" />
diff --git a/unity/Assets/Ably/Examples/Dashboard/AblyMain.cs b/unity/Assets/Ably/Examples/Dashboard/AblyMain.cs
index be9536ec7..3b0f6e929 100644
--- a/unity/Assets/Ably/Examples/Dashboard/AblyMain.cs
+++ b/unity/Assets/Ably/Examples/Dashboard/AblyMain.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Threading;
 using IO.Ably;
+using IO.Ably.PubSub.Device;
 using IO.Ably.Realtime;
 using UnityEngine;
 using UnityEngine.UI;
@@ -54,7 +55,7 @@ private void InitializeAbly()
                 CustomContext = SynchronizationContext.Current
             };
 
-            _ably = new AblyRealtime(_clientOptions);
+            _ably = PubSubDevice.CreateClient(_clientOptions);
             _ably.Connection.On(args =>
             {
                 LogAndDisplay($"Connection State is <b>{args.Current}</b>");
diff --git a/unity/Assets/Ably/Plugins/Ably.PubSub.Device.dll b/unity/Assets/Ably/Plugins/Ably.PubSub.Device.dll
new file mode 100644
index 000000000..2df3a14ef
Binary files /dev/null and b/unity/Assets/Ably/Plugins/Ably.PubSub.Device.dll differ
diff --git a/unity/Assets/Ably/Plugins/Ably.PubSub.Core.dll.meta b/unity/Assets/Ably/Plugins/Ably.PubSub.Device.dll.meta
similarity index 100%
rename from unity/Assets/Ably/Plugins/Ably.PubSub.Core.dll.meta
rename to unity/Assets/Ably/Plugins/Ably.PubSub.Device.dll.meta
diff --git a/unity/Assets/Ably/Plugins/link.xml b/unity/Assets/Ably/Plugins/link.xml
index 39b1151c8..ab718682e 100644
--- a/unity/Assets/Ably/Plugins/link.xml
+++ b/unity/Assets/Ably/Plugins/link.xml
@@ -1,5 +1,5 @@
 <linker>
-    <assembly fullname="Ably.PubSub.Core" preserve="all" />
+    <assembly fullname="Ably.PubSub.Device" preserve="all" />
     <assembly fullname="UnityEngine.CoreModule">
         <type fullname="UnityEngine.Application">
             <property name="unityVersion" />
diff --git a/unity/Assets/Tests/AblySandbox/AblySandbox.asmdef b/unity/Assets/Tests/AblySandbox/AblySandbox.asmdef
index 426714cbd..7aa3db832 100644
--- a/unity/Assets/Tests/AblySandbox/AblySandbox.asmdef
+++ b/unity/Assets/Tests/AblySandbox/AblySandbox.asmdef
@@ -8,7 +8,7 @@
     "overrideReferences": true,
     "precompiledReferences": [
         "nunit.framework.dll",
-        "Ably.PubSub.Core.dll"
+        "Ably.PubSub.Device.dll"
     ],
     "autoReferenced": false,
     "defineConstraints": [
diff --git a/unity/Assets/Tests/EditMode/AblyRealtimeSpecs.cs b/unity/Assets/Tests/EditMode/AblyRealtimeSpecs.cs
index b3aa4d3b5..45c92dda1 100644
--- a/unity/Assets/Tests/EditMode/AblyRealtimeSpecs.cs
+++ b/unity/Assets/Tests/EditMode/AblyRealtimeSpecs.cs
@@ -227,7 +227,7 @@ public IEnumerator TestHttpUnityAgentHeader([ValueSource(nameof(_protocols))] Pr
 
                 var keys = new List<string>()
                 {
-                    "ably-dotnet/",
+                    "ably-pubsub-dotnet/",
                     Agent.DotnetRuntimeIdentifier,
                     UnityHelper.UnityIdentifier,
                     Agent.OsIdentifier
diff --git a/unity/Assets/Tests/EditMode/EditMode.asmdef b/unity/Assets/Tests/EditMode/EditMode.asmdef
index a9a72e2f2..60c0711e7 100644
--- a/unity/Assets/Tests/EditMode/EditMode.asmdef
+++ b/unity/Assets/Tests/EditMode/EditMode.asmdef
@@ -15,7 +15,7 @@
     "overrideReferences": false,
     "precompiledReferences": [
         "nunit.framework.dll",
-        "Ably.PubSub.Core.dll"
+        "Ably.PubSub.Device.dll"
     ],
     "autoReferenced": false,
     "defineConstraints": [
diff --git a/unity/Assets/Tests/PlayMode/AblyRealtimeSpecs.cs b/unity/Assets/Tests/PlayMode/AblyRealtimeSpecs.cs
index b465901a3..87d5fc81a 100644
--- a/unity/Assets/Tests/PlayMode/AblyRealtimeSpecs.cs
+++ b/unity/Assets/Tests/PlayMode/AblyRealtimeSpecs.cs
@@ -227,7 +227,7 @@ public IEnumerator TestHttpUnityAgentHeader([ValueSource(nameof(_protocols))] Pr
 
                 var keys = new List<string>()
                 {
-                    "ably-dotnet/",
+                    "ably-pubsub-dotnet/",
                     Agent.DotnetRuntimeIdentifier,
                     UnityHelper.UnityIdentifier,
                     Agent.OsIdentifier
diff --git a/unity/Assets/Tests/PlayMode/PlayMode.asmdef b/unity/Assets/Tests/PlayMode/PlayMode.asmdef
index 89dbf3eb2..810c7cf2e 100644
--- a/unity/Assets/Tests/PlayMode/PlayMode.asmdef
+++ b/unity/Assets/Tests/PlayMode/PlayMode.asmdef
@@ -14,7 +14,7 @@
     "overrideReferences": true,
     "precompiledReferences": [
         "nunit.framework.dll",
-        "Ably.PubSub.Core.dll"
+        "Ably.PubSub.Device.dll"
     ],
     "autoReferenced": false,
     "defineConstraints": [
diff --git a/unity/CONTRIBUTING.md b/unity/CONTRIBUTING.md
index e3bd7709c..8d5b44064 100644
--- a/unity/CONTRIBUTING.md
+++ b/unity/CONTRIBUTING.md
@@ -151,4 +151,4 @@ Unity.exe -batchmode -nographics -quit -projectPath 'C:\Users\${UserName}\UnityP
 ## Updating the Ably Unity Package
 - Currently, the latest Ably source code is imported as DLLs in Unity using [Unity Plug-ins](https://docs.unity3d.com/Manual/Plugins.html).
 - This is done as part of the [release process](../CONTRIBUTING.md/#release-process) by running `./unity-plugins-updater.sh 1.2.3` (linux/mac) / `.\unity-plugins-updater.cmd 1.2.3` (windows) at the root.
-- This script is responsible for merging all dependencies into `Ably.PubSub.Core.dll` and copying it to `unity/Assets/Ably/Plugins/`.
+- This script is responsible for merging all dependencies into `Ably.PubSub.Device.dll` (the core plus the device door and dependencies, merged) and copying it to `unity/Assets/Ably/Plugins/`.
diff --git a/unity/README.md b/unity/README.md
index d8034b733..366bbffe9 100644
--- a/unity/README.md
+++ b/unity/README.md
@@ -18,6 +18,7 @@
 using System;
 using System.Threading;
 using IO.Ably;
+using IO.Ably.PubSub.Device;
 using IO.Ably.Realtime;
 using UnityEngine;
 using UnityEngine.UI;
@@ -48,7 +49,7 @@ namespace Example.ChatApp
                 CustomContext = SynchronizationContext.Current
             };
 
-            _ably = new AblyRealtime(_clientOptions);
+            _ably = PubSubDevice.CreateClient(_clientOptions);
             _ably.Connection.On(args =>
             {
                 Debug.Log($"Connection State is <b>{args.Current}</b>");