diff --git a/temporal/api/nexusservices/workerservice/v1/request_response.proto b/temporal/api/nexusservices/workerservice/v1/request_response.proto
new file mode 100644
index 000000000..ef14decbd
--- /dev/null
+++ b/temporal/api/nexusservices/workerservice/v1/request_response.proto
@@ -0,0 +1,46 @@
+syntax = "proto3";
+
+package temporal.api.nexusservices.workerservice.v1;
+
+option go_package = "go.temporal.io/api/nexusservices/workerservice/v1;workerservice";
+option java_package = "io.temporal.api.nexusservices.workerservice.v1";
+option java_multiple_files = true;
+option java_outer_classname = "RequestResponseProto";
+option ruby_package = "Temporalio::Api::Nexusservices::Workerservice::V1";
+option csharp_namespace = "Temporalio.Api.Nexusservices.Workerservice.V1";
+
+// (--
+// Internal Nexus service for server-to-worker communication.
+// See service.yaml for the service definition.
+// --)
+
+// Request payload for the "executeCommands" Nexus operation.
+message WorkerCommandsRequest {
+    repeated WorkerCommand commands = 1;
+
+    message WorkerCommand {
+        oneof type {
+            CancelActivity cancel_activity = 1;
+        }
+    }
+
+    // Cancel an activity if it is still running. Otherwise, do nothing.
+    message CancelActivity {
+        bytes task_token = 1;
+    }
+}
+
+// Response payload for the "executeCommands" Nexus operation.
+message WorkerCommandsResponse {
+    repeated WorkerCommandResult results = 1;
+
+    message WorkerCommandResult {
+        oneof type {
+            CancelActivity cancel_activity = 1;
+        }
+    }
+
+    // Treat both successful cancellation and no-op (activity is no longer running) as success.
+    message CancelActivity {
+    }
+}
diff --git a/temporal/api/nexusservices/workerservice/v1/service.yaml b/temporal/api/nexusservices/workerservice/v1/service.yaml
new file mode 100644
index 000000000..ad42b3bba
--- /dev/null
+++ b/temporal/api/nexusservices/workerservice/v1/service.yaml
@@ -0,0 +1,32 @@
+# yaml-language-server: $schema=https://raw.githubusercontent.com/nexus-rpc/nexus-rpc-gen/main/schemas/nexus-rpc-gen.json
+#
+# Nexus service definition for server-to-worker communication.
+# See request_response.proto for message definitions.
+#
+# Task queue format: /temporal-sys/worker-commands/{namespace}/{worker_grouping_key}
+
+nexusrpc: 1.0.0
+
+services:
+  temporal.api.nexusservices.workerservice.v1.WorkerService:
+    description: >
+      Internal Nexus service for server-to-worker communication.
+      Used by the Temporal server to send commands to workers.
+    operations:
+      executeCommands:
+        description: Executes worker commands sent by the server.
+        input:
+          $goRef: "go.temporal.io/api/nexusservices/workerservice/v1.WorkerCommandsRequest"
+          $javaRef: "io.temporal.api.nexusservices.workerservice.v1.WorkerCommandsRequest"
+          $pythonRef: "temporalio.api.nexusservices.workerservice.v1.WorkerCommandsRequest"
+          $typescriptRef: "@temporalio/api/nexusservices/workerservice/v1.WorkerCommandsRequest"
+          $dotnetRef: "Temporalio.Api.Nexusservices.Workerservice.V1.WorkerCommandsRequest"
+          $rubyRef: "Temporalio::Api::Nexusservices::Workerservice::V1::WorkerCommandsRequest"
+        output:
+          $goRef: "go.temporal.io/api/nexusservices/workerservice/v1.WorkerCommandsResponse"
+          $javaRef: "io.temporal.api.nexusservices.workerservice.v1.WorkerCommandsResponse"
+          $pythonRef: "temporalio.api.nexusservices.workerservice.v1.WorkerCommandsResponse"
+          $typescriptRef: "@temporalio/api/nexusservices/workerservice/v1.WorkerCommandsResponse"
+          $dotnetRef: "Temporalio.Api.Nexusservices.Workerservice.V1.WorkerCommandsResponse"
+          $rubyRef: "Temporalio::Api::Nexusservices::Workerservice::V1::WorkerCommandsResponse"
+