diff --git a/packages/toolbox-adk/integration.cloudbuild.yaml b/packages/toolbox-adk/integration.cloudbuild.yaml
index ff1b1c1f5..3bdf3fa4a 100644
--- a/packages/toolbox-adk/integration.cloudbuild.yaml
+++ b/packages/toolbox-adk/integration.cloudbuild.yaml
@@ -50,5 +50,5 @@ options:
 substitutions:
   _VERSION: '3.13'
   # Default values (can be overridden by triggers)
-  _TOOLBOX_VERSION: '1.4.0'
+  _TOOLBOX_VERSION: 'v1.6.0'
   _TOOLBOX_MANIFEST_VERSION: '34'
diff --git a/packages/toolbox-adk/pyproject.toml b/packages/toolbox-adk/pyproject.toml
index 3ad5c35e4..52072abf8 100644
--- a/packages/toolbox-adk/pyproject.toml
+++ b/packages/toolbox-adk/pyproject.toml
@@ -40,6 +40,7 @@ test = [
     "pytest==9.0.3",
     "pytest-asyncio==1.4.0",
     "pytest-cov==7.1.0",
+    "numpy<2.2.0",
     "pytest-mock==3.15.1"
 ]
 
diff --git a/packages/toolbox-adk/src/toolbox_adk/tool.py b/packages/toolbox-adk/src/toolbox_adk/tool.py
index db41f81b9..0d94821b6 100644
--- a/packages/toolbox-adk/src/toolbox_adk/tool.py
+++ b/packages/toolbox-adk/src/toolbox_adk/tool.py
@@ -17,11 +17,7 @@
 from typing import Any, Awaitable, Callable, Dict, Mapping, Optional
 
 import toolbox_core
-from fastapi.openapi.models import (
-    OAuth2,
-    OAuthFlowAuthorizationCode,
-    OAuthFlows,
-)
+from fastapi.openapi.models import OAuth2, OAuthFlowAuthorizationCode, OAuthFlows
 from google.adk.auth.auth_credential import (
     AuthCredential,
     AuthCredentialTypes,
diff --git a/packages/toolbox-adk/tests/integration/conftest.py b/packages/toolbox-adk/tests/integration/conftest.py
index 7a0346c3a..20aea226d 100644
--- a/packages/toolbox-adk/tests/integration/conftest.py
+++ b/packages/toolbox-adk/tests/integration/conftest.py
@@ -25,7 +25,7 @@
 from typing import Generator
 
 import google
-import pytest_asyncio
+import pytest
 from google.auth import compute_engine
 from google.cloud import secretmanager, storage
 
@@ -75,7 +75,8 @@ def get_toolbox_binary_url(toolbox_version: str) -> str:
     arch = (
         "arm64" if os_system == "darwin" and platform.machine() == "arm64" else "amd64"
     )
-    return f"v{toolbox_version}/{os_system}/{arch}/toolbox"
+    ext = ".exe" if os_system == "windows" else ""
+    return f"{toolbox_version}/{os_system}/{arch}/toolbox{ext}"
 
 
 def get_auth_token(client_id: str) -> str:
@@ -92,17 +93,17 @@ def get_auth_token(client_id: str) -> str:
 
 
 #### Define Fixtures
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def project_id() -> str:
     return get_env_var("GOOGLE_CLOUD_PROJECT")
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def toolbox_version() -> str:
     return get_env_var("TOOLBOX_VERSION")
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def tools_file_path(project_id: str) -> Generator[str]:
     """Provides a temporary file path containing the tools manifest."""
     if os.environ.get("TEST_MOCK_GCP"):
@@ -122,7 +123,7 @@ def tools_file_path(project_id: str) -> Generator[str]:
     os.remove(tools_file_path)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def auth_token1(project_id: str) -> str:
     if os.environ.get("TEST_MOCK_GCP"):
         return "mock-token-1"
@@ -132,7 +133,7 @@ def auth_token1(project_id: str) -> str:
     return get_auth_token(client_id)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def auth_token2(project_id: str) -> str:
     if os.environ.get("TEST_MOCK_GCP"):
         return "mock-token-2"
@@ -142,7 +143,7 @@ def auth_token2(project_id: str) -> str:
     return get_auth_token(client_id)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None]:
     """Starts the toolbox server as a subprocess."""
     if os.environ.get("TEST_MOCK_GCP"):
@@ -151,7 +152,12 @@ def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None
 
     print("Downloading toolbox binary from gcs bucket...")
     source_blob_name = get_toolbox_binary_url(toolbox_version)
-    download_blob("mcp-toolbox-for-databases", source_blob_name, "toolbox")
+    bucket_name = (
+        "mcp-toolbox-for-databases-dev"
+        if toolbox_version in ("main", "mcp-v202606")
+        else "mcp-toolbox-for-databases"
+    )
+    download_blob(bucket_name, source_blob_name, "toolbox")
 
     print("Toolbox binary downloaded successfully.")
     try:
@@ -159,20 +165,30 @@ def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None
         # Make toolbox executable
         os.chmod("toolbox", 0o700)
         # Run toolbox binary
-        toolbox_server = subprocess.Popen(
-            ["./toolbox", "--tools-file", tools_file_path]
+        toolbox_server_1 = subprocess.Popen(
+            ["./toolbox", "--port", "5000", "--tools-file", tools_file_path]
+        )
+        toolbox_server_2 = subprocess.Popen(
+            [
+                "./toolbox",
+                "--port",
+                "5001",
+                "--tools-file",
+                tools_file_path,
+                "--enable-draft-specs",
+            ]
         )
 
         # Wait for server to start
         # Retry logic with a timeout
         for _ in range(5):  # retries
             time.sleep(2)
-            print("Checking if toolbox is successfully started...")
-            if toolbox_server.poll() is None:
-                print("Toolbox server started successfully.")
+            print("Checking if both toolbox servers are successfully started...")
+            if toolbox_server_1.poll() is None and toolbox_server_2.poll() is None:
+                print("Toolbox servers started successfully.")
                 break
         else:
-            raise RuntimeError("Toolbox server failed to start after 5 retries.")
+            raise RuntimeError("Toolbox servers failed to start after 5 retries.")
     except subprocess.CalledProcessError as e:
         print(e.stderr.decode("utf-8"))
         print(e.stdout.decode("utf-8"))
@@ -180,5 +196,31 @@ def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None
     yield
 
     # Clean up toolbox server
-    toolbox_server.terminate()
-    toolbox_server.wait(timeout=5)
+    toolbox_server_1.terminate()
+    toolbox_server_2.terminate()
+    toolbox_server_1.wait(timeout=5)
+    toolbox_server_2.wait(timeout=5)
+
+
+@pytest.fixture(
+    params=["http://localhost:5000", "http://localhost:5001"], scope="session"
+)
+def toolbox_server_url(request) -> str:
+    return request.param
+
+
+@pytest.fixture(autouse=True)
+def patch_toolbox_client_url(toolbox_server_url):
+    from toolbox_adk.toolset import ToolboxToolset
+
+    original_init = ToolboxToolset.__init__
+
+    def new_init(self, server_url="http://localhost:5000", *args, **kwargs):
+        if server_url == "http://localhost:5000":
+            server_url = toolbox_server_url
+        original_init(self, server_url, *args, **kwargs)
+
+    from unittest.mock import patch
+
+    with patch.object(ToolboxToolset, "__init__", new_init, create=True):
+        yield
diff --git a/packages/toolbox-adk/tests/unit/test_credentials.py b/packages/toolbox-adk/tests/unit/test_credentials.py
index 749d28667..9e94d5638 100644
--- a/packages/toolbox-adk/tests/unit/test_credentials.py
+++ b/packages/toolbox-adk/tests/unit/test_credentials.py
@@ -109,10 +109,7 @@ def test_from_adk_credentials_http_bearer(self):
 
     def test_from_adk_credentials_api_key(self):
         from fastapi.openapi.models import APIKey, APIKeyIn
-        from google.adk.auth.auth_credential import (
-            AuthCredential,
-            AuthCredentialTypes,
-        )
+        from google.adk.auth.auth_credential import AuthCredential, AuthCredentialTypes
 
         auth_credential = AuthCredential(
             auth_type=AuthCredentialTypes.API_KEY, api_key="abc"
@@ -129,10 +126,7 @@ def test_from_adk_credentials_api_key(self):
 
     def test_from_adk_credentials_api_key_default_location(self):
         from fastapi.openapi.models import APIKey
-        from google.adk.auth.auth_credential import (
-            AuthCredential,
-            AuthCredentialTypes,
-        )
+        from google.adk.auth.auth_credential import AuthCredential, AuthCredentialTypes
 
         auth_credential = AuthCredential(
             auth_type=AuthCredentialTypes.API_KEY, api_key="abc"
@@ -157,10 +151,7 @@ class MockScheme:
     def test_from_adk_credentials_api_key_query_fail(self):
         import pytest
         from fastapi.openapi.models import APIKey, APIKeyIn
-        from google.adk.auth.auth_credential import (
-            AuthCredential,
-            AuthCredentialTypes,
-        )
+        from google.adk.auth.auth_credential import AuthCredential, AuthCredentialTypes
 
         cred = AuthCredential(auth_type=AuthCredentialTypes.API_KEY, api_key="abc")
         scheme = APIKey(type="apiKey", name="key", **{"in": APIKeyIn.query})
@@ -172,10 +163,7 @@ def test_from_adk_credentials_api_key_query_fail(self):
 
     def test_from_adk_credentials_api_key_no_scheme_raises(self):
         import pytest
-        from google.adk.auth.auth_credential import (
-            AuthCredential,
-            AuthCredentialTypes,
-        )
+        from google.adk.auth.auth_credential import AuthCredential, AuthCredentialTypes
 
         auth_credential = AuthCredential(
             auth_type=AuthCredentialTypes.API_KEY, api_key="my-key"
@@ -187,10 +175,7 @@ def test_from_adk_credentials_api_key_no_scheme_raises(self):
 
     def test_from_adk_credentials_unsupported(self):
         import pytest
-        from google.adk.auth.auth_credential import (
-            AuthCredential,
-            AuthCredentialTypes,
-        )
+        from google.adk.auth.auth_credential import AuthCredential, AuthCredentialTypes
 
         auth_credential = AuthCredential(
             auth_type=AuthCredentialTypes.OAUTH2
diff --git a/packages/toolbox-core/integration.cloudbuild.yaml b/packages/toolbox-core/integration.cloudbuild.yaml
index de5f69465..a384d4de7 100644
--- a/packages/toolbox-core/integration.cloudbuild.yaml
+++ b/packages/toolbox-core/integration.cloudbuild.yaml
@@ -45,5 +45,5 @@ options:
   logging: CLOUD_LOGGING_ONLY
 substitutions:
   _VERSION: '3.13'
-  _TOOLBOX_VERSION: '1.4.0'
+  _TOOLBOX_VERSION: 'v1.6.0'
   _TOOLBOX_MANIFEST_VERSION: '34'
diff --git a/packages/toolbox-core/pyproject.toml b/packages/toolbox-core/pyproject.toml
index 6c2bf1a6d..21237a970 100644
--- a/packages/toolbox-core/pyproject.toml
+++ b/packages/toolbox-core/pyproject.toml
@@ -56,6 +56,7 @@ test = [
     "pytest-aioresponses==0.3.0",
     "pytest-asyncio==1.4.0",
     "pytest-cov==7.1.0",
+    "numpy<2.2.0",
     "pytest-mock==3.15.1",
     "google-cloud-secret-manager==2.28.0",
     "google-cloud-storage==3.10.1",
diff --git a/packages/toolbox-core/src/toolbox_core/client.py b/packages/toolbox-core/src/toolbox_core/client.py
index 641e80599..b2224eedc 100644
--- a/packages/toolbox-core/src/toolbox_core/client.py
+++ b/packages/toolbox-core/src/toolbox_core/client.py
@@ -63,7 +63,7 @@ def __init__(
 
     def _create_transport(self, protocol: Protocol) -> ITransport:
         match protocol:
-            case Protocol.MCP_LATEST:
+            case Protocol.MCP_DRAFT:
                 return McpHttpTransportV20260618(
                     self._url,
                     self._session,
diff --git a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20241105/mcp.py b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20241105/mcp.py
index ec6a2475d..7f03dcee0 100644
--- a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20241105/mcp.py
+++ b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20241105/mcp.py
@@ -18,6 +18,7 @@
 from pydantic import BaseModel
 
 from ... import version
+from ...exceptions import ProtocolNegotiationError
 from ...protocol import ManifestSchema, TelemetryAttributes
 from .. import telemetry
 from ..transport_base import _McpHttpTransportBase
@@ -131,9 +132,7 @@ async def _initialize_session(
             self._server_version = result.serverInfo.version
 
             if result.protocolVersion != self._protocol_version:
-                raise RuntimeError(
-                    f"MCP version mismatch: client does not support server version {result.protocolVersion}"
-                )
+                raise ProtocolNegotiationError(result.protocolVersion)
 
             if not result.capabilities.tools:
                 if self._manage_session:
diff --git a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250326/mcp.py b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250326/mcp.py
index 0194bd282..a28f9db0e 100644
--- a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250326/mcp.py
+++ b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250326/mcp.py
@@ -18,6 +18,7 @@
 from pydantic import BaseModel
 
 from ... import version
+from ...exceptions import ProtocolNegotiationError
 from ...protocol import ManifestSchema, TelemetryAttributes
 from .. import telemetry
 from ..transport_base import _McpHttpTransportBase
@@ -147,10 +148,7 @@ async def _initialize_session(
             self._server_version = result.serverInfo.version
 
             if result.protocolVersion != self._protocol_version:
-                raise RuntimeError(
-                    "MCP version mismatch: client does not support server version"
-                    f" {result.protocolVersion}"
-                )
+                raise ProtocolNegotiationError(result.protocolVersion)
 
             if not result.capabilities.tools:
                 if self._manage_session:
diff --git a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250618/mcp.py b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250618/mcp.py
index d7a626ed1..11a471ecf 100644
--- a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250618/mcp.py
+++ b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250618/mcp.py
@@ -18,6 +18,7 @@
 from pydantic import BaseModel
 
 from ... import version
+from ...exceptions import ProtocolNegotiationError
 from ...protocol import ManifestSchema, TelemetryAttributes
 from .. import telemetry
 from ..transport_base import _McpHttpTransportBase
@@ -138,10 +139,7 @@ async def _initialize_session(
             self._server_version = result.serverInfo.version
 
             if result.protocolVersion != self._protocol_version:
-                raise RuntimeError(
-                    "MCP version mismatch: client does not support server version"
-                    f" {result.protocolVersion}"
-                )
+                raise ProtocolNegotiationError(result.protocolVersion)
 
             if not result.capabilities.tools:
                 if self._manage_session:
diff --git a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20251125/mcp.py b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20251125/mcp.py
index 999301552..1bf741e76 100644
--- a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20251125/mcp.py
+++ b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20251125/mcp.py
@@ -18,6 +18,7 @@
 from pydantic import BaseModel
 
 from ... import version
+from ...exceptions import ProtocolNegotiationError
 from ...protocol import ManifestSchema, TelemetryAttributes
 from .. import telemetry
 from ..transport_base import _McpHttpTransportBase
@@ -138,10 +139,7 @@ async def _initialize_session(
             self._server_version = result.serverInfo.version
 
             if result.protocolVersion != self._protocol_version:
-                raise RuntimeError(
-                    "MCP version mismatch: client does not support server version"
-                    f" {result.protocolVersion}"
-                )
+                raise ProtocolNegotiationError(result.protocolVersion)
 
             if not result.capabilities.tools:
                 if self._manage_session:
diff --git a/packages/toolbox-core/src/toolbox_core/protocol.py b/packages/toolbox-core/src/toolbox_core/protocol.py
index 57d12fb33..350e0251f 100644
--- a/packages/toolbox-core/src/toolbox_core/protocol.py
+++ b/packages/toolbox-core/src/toolbox_core/protocol.py
@@ -51,14 +51,17 @@ class Protocol(str, Enum):
     MCP_v20250326 = "2025-03-26"
     MCP_v20241105 = "2024-11-05"
     MCP_v20251125 = "2025-11-25"
-    MCP = MCP_v20250618
-    MCP_LATEST = "DRAFT-2026-v1"
+    MCP_v2026_DRAFT = "DRAFT-2026-v1"
+
+    MCP = MCP_v20251125
+    MCP_LATEST = MCP_v20251125
+    MCP_DRAFT = MCP_v2026_DRAFT
 
     @staticmethod
     def get_supported_mcp_versions() -> list[str]:
         """Returns a list of supported MCP protocol versions."""
         return [
-            Protocol.MCP_LATEST.value,
+            Protocol.MCP_DRAFT.value,
             Protocol.MCP_v20251125.value,
             Protocol.MCP_v20250618.value,
             Protocol.MCP_v20250326.value,
diff --git a/packages/toolbox-core/tests/conftest.py b/packages/toolbox-core/tests/conftest.py
index 338d031c0..2e500752e 100644
--- a/packages/toolbox-core/tests/conftest.py
+++ b/packages/toolbox-core/tests/conftest.py
@@ -25,7 +25,7 @@
 from typing import Generator
 
 import google
-import pytest_asyncio
+import pytest
 from google.auth import compute_engine
 from google.cloud import secretmanager, storage
 
@@ -75,7 +75,8 @@ def get_toolbox_binary_url(toolbox_version: str) -> str:
     arch = (
         "arm64" if os_system == "darwin" and platform.machine() == "arm64" else "amd64"
     )
-    return f"v{toolbox_version}/{os_system}/{arch}/toolbox"
+    ext = ".exe" if os_system == "windows" else ""
+    return f"{toolbox_version}/{os_system}/{arch}/toolbox{ext}"
 
 
 def get_auth_token(client_id: str) -> str:
@@ -92,17 +93,17 @@ def get_auth_token(client_id: str) -> str:
 
 
 #### Define Fixtures
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def project_id() -> str:
     return get_env_var("GOOGLE_CLOUD_PROJECT")
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def toolbox_version() -> str:
     return get_env_var("TOOLBOX_VERSION")
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def tools_file_path(project_id: str) -> Generator[str]:
     """Provides a temporary file path containing the tools manifest."""
     tools_manifest = access_secret_version(
@@ -115,7 +116,7 @@ def tools_file_path(project_id: str) -> Generator[str]:
     os.remove(tools_file_path)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def auth_token1(project_id: str) -> str:
     client_id = access_secret_version(
         project_id=project_id, secret_id="sdk_testing_client1"
@@ -123,7 +124,7 @@ def auth_token1(project_id: str) -> str:
     return get_auth_token(client_id)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def auth_token2(project_id: str) -> str:
     client_id = access_secret_version(
         project_id=project_id, secret_id="sdk_testing_client2"
@@ -131,32 +132,47 @@ def auth_token2(project_id: str) -> str:
     return get_auth_token(client_id)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None]:
     """Starts the toolbox server as a subprocess."""
     print("Downloading toolbox binary from gcs bucket...")
     source_blob_name = get_toolbox_binary_url(toolbox_version)
-    download_blob("mcp-toolbox-for-databases", source_blob_name, "toolbox")
+    bucket_name = (
+        "mcp-toolbox-for-databases-dev"
+        if toolbox_version in ("main", "mcp-v202606")
+        else "mcp-toolbox-for-databases"
+    )
+    download_blob(bucket_name, source_blob_name, "toolbox")
     print("Toolbox binary downloaded successfully.")
     try:
         print("Opening toolbox server process...")
         # Make toolbox executable
         os.chmod("toolbox", 0o700)
         # Run toolbox binary
-        toolbox_server = subprocess.Popen(
-            ["./toolbox", "--tools-file", tools_file_path]
+        toolbox_server_1 = subprocess.Popen(
+            ["./toolbox", "--port", "5000", "--tools-file", tools_file_path]
+        )
+        toolbox_server_2 = subprocess.Popen(
+            [
+                "./toolbox",
+                "--port",
+                "5001",
+                "--tools-file",
+                tools_file_path,
+                "--enable-draft-specs",
+            ]
         )
 
         # Wait for server to start
         # Retry logic with a timeout
         for _ in range(5):  # retries
             time.sleep(2)
-            print("Checking if toolbox is successfully started...")
-            if toolbox_server.poll() is None:
-                print("Toolbox server started successfully.")
+            print("Checking if both toolbox servers are successfully started...")
+            if toolbox_server_1.poll() is None and toolbox_server_2.poll() is None:
+                print("Toolbox servers started successfully.")
                 break
         else:
-            raise RuntimeError("Toolbox server failed to start after 5 retries.")
+            raise RuntimeError("Toolbox servers failed to start after 5 retries.")
     except subprocess.CalledProcessError as e:
         print(e.stderr.decode("utf-8"))
         print(e.stdout.decode("utf-8"))
@@ -164,5 +180,39 @@ def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None
     yield
 
     # Clean up toolbox server
-    toolbox_server.terminate()
-    toolbox_server.wait(timeout=5)
+    toolbox_server_1.terminate()
+    toolbox_server_2.terminate()
+    toolbox_server_1.wait(timeout=5)
+    toolbox_server_2.wait(timeout=5)
+
+
+@pytest.fixture(
+    params=["http://localhost:5000", "http://localhost:5001"], scope="session"
+)
+def toolbox_server_url(request) -> str:
+    return request.param
+
+
+@pytest.fixture(autouse=True)
+def patch_toolbox_client_url(toolbox_server_url):
+    from toolbox_core.client import ToolboxClient
+    from toolbox_core.sync_client import ToolboxSyncClient
+
+    original_init = ToolboxClient.__init__
+    original_sync_init = ToolboxSyncClient.__init__
+
+    def new_init(self, url="http://localhost:5000", *args, **kwargs):
+        if url == "http://localhost:5000":
+            url = toolbox_server_url
+        original_init(self, url, *args, **kwargs)
+
+    def new_sync_init(self, url="http://localhost:5000", *args, **kwargs):
+        if url == "http://localhost:5000":
+            url = toolbox_server_url
+        original_sync_init(self, url, *args, **kwargs)
+
+    from unittest.mock import patch
+
+    with patch.object(ToolboxClient, "__init__", new_init, create=True):
+        with patch.object(ToolboxSyncClient, "__init__", new_sync_init, create=True):
+            yield
diff --git a/packages/toolbox-core/tests/mcp_transport/test_v20241105.py b/packages/toolbox-core/tests/mcp_transport/test_v20241105.py
index 1ce2f39bb..eadb0e264 100644
--- a/packages/toolbox-core/tests/mcp_transport/test_v20241105.py
+++ b/packages/toolbox-core/tests/mcp_transport/test_v20241105.py
@@ -18,6 +18,7 @@
 import pytest_asyncio
 from aiohttp import ClientSession
 
+from toolbox_core.exceptions import ProtocolNegotiationError
 from toolbox_core.mcp_transport.v20241105 import types
 from toolbox_core.mcp_transport.v20241105.mcp import McpHttpTransportV20241105
 from toolbox_core.protocol import ManifestSchema, Protocol
@@ -248,7 +249,7 @@ async def test_initialize_session_protocol_mismatch(self, transport, mocker):
             ),
         )
 
-        with pytest.raises(RuntimeError, match="MCP version mismatch"):
+        with pytest.raises(ProtocolNegotiationError):
             await transport._initialize_session()
 
     async def test_initialize_session_missing_tools_capability(self, transport, mocker):
diff --git a/packages/toolbox-core/tests/mcp_transport/test_v20250618.py b/packages/toolbox-core/tests/mcp_transport/test_v20250618.py
index fd2e50f7c..b5a1a0a94 100644
--- a/packages/toolbox-core/tests/mcp_transport/test_v20250618.py
+++ b/packages/toolbox-core/tests/mcp_transport/test_v20250618.py
@@ -18,6 +18,7 @@
 import pytest_asyncio
 from aiohttp import ClientSession
 
+from toolbox_core.exceptions import ProtocolNegotiationError
 from toolbox_core.mcp_transport.v20250618 import types
 from toolbox_core.mcp_transport.v20250618.mcp import McpHttpTransportV20250618
 from toolbox_core.protocol import ManifestSchema, Protocol, TelemetryAttributes
@@ -256,7 +257,7 @@ async def test_initialize_session_protocol_mismatch(self, transport, mocker):
             ),
         )
 
-        with pytest.raises(RuntimeError, match="MCP version mismatch"):
+        with pytest.raises(ProtocolNegotiationError):
             await transport._initialize_session()
 
     async def test_initialize_session_missing_tools_capability(self, transport, mocker):
diff --git a/packages/toolbox-core/tests/mcp_transport/test_v20251125.py b/packages/toolbox-core/tests/mcp_transport/test_v20251125.py
index 9942041aa..f575b81bc 100644
--- a/packages/toolbox-core/tests/mcp_transport/test_v20251125.py
+++ b/packages/toolbox-core/tests/mcp_transport/test_v20251125.py
@@ -18,6 +18,7 @@
 import pytest_asyncio
 from aiohttp import ClientSession
 
+from toolbox_core.exceptions import ProtocolNegotiationError
 from toolbox_core.mcp_transport.v20251125 import types
 from toolbox_core.mcp_transport.v20251125.mcp import McpHttpTransportV20251125
 from toolbox_core.protocol import ManifestSchema, Protocol
@@ -256,7 +257,7 @@ async def test_initialize_session_protocol_mismatch(self, transport, mocker):
             ),
         )
 
-        with pytest.raises(RuntimeError, match="MCP version mismatch"):
+        with pytest.raises(ProtocolNegotiationError):
             await transport._initialize_session()
 
     async def test_initialize_session_missing_tools_capability(self, transport, mocker):
diff --git a/packages/toolbox-core/tests/mcp_transport/test_v20260618.py b/packages/toolbox-core/tests/mcp_transport/test_v20260618.py
index 40d1842e7..5c751320f 100644
--- a/packages/toolbox-core/tests/mcp_transport/test_v20260618.py
+++ b/packages/toolbox-core/tests/mcp_transport/test_v20260618.py
@@ -70,7 +70,7 @@ async def transport(request, mocker):
     transport = McpHttpTransportV20260618(
         "http://fake-server.com",
         session=mock_session,
-        protocol=Protocol.MCP_LATEST,
+        protocol=Protocol.MCP_DRAFT,
         telemetry_enabled=request.param,
     )
     yield transport
diff --git a/packages/toolbox-core/tests/test_client.py b/packages/toolbox-core/tests/test_client.py
index 20690eb46..e28bb03a1 100644
--- a/packages/toolbox-core/tests/test_client.py
+++ b/packages/toolbox-core/tests/test_client.py
@@ -276,7 +276,7 @@ async def test_load_tool_protocol_fallback_success(test_tool_str):
         mock_2025.tool_invoke.return_value = "ok_from_fallback"
         mock_2025_cls.return_value = mock_2025
 
-        async with ToolboxClient(TEST_BASE_URL, protocol=Protocol.MCP_LATEST) as client:
+        async with ToolboxClient(TEST_BASE_URL, protocol=Protocol.MCP_DRAFT) as client:
             # This should trigger the fallback
             loaded_tool = await client.load_tool(TOOL_NAME)
 
@@ -320,7 +320,7 @@ async def test_load_tool_protocol_fallback_infinite_loop_prevention(test_tool_st
         mock_2025.tool_get.side_effect = ProtocolNegotiationError("2024-11-05")
         mock_2025_cls.return_value = mock_2025
 
-        async with ToolboxClient(TEST_BASE_URL, protocol=Protocol.MCP_LATEST) as client:
+        async with ToolboxClient(TEST_BASE_URL, protocol=Protocol.MCP_DRAFT) as client:
             with pytest.raises(
                 ProtocolNegotiationError,
                 match="Server requires protocol fallback to 2024-11-05",
@@ -810,7 +810,7 @@ async def test_client_init_with_client_info():
 def test_toolbox_client_no_warning_on_mcp():
     """Test that initializing ToolboxClient with Protocol.MCP issues NO DeprecationWarning."""
     # Mock the transport to avoid actual connection attempts or MCP version warnings
-    with patch("toolbox_core.client.McpHttpTransportV20250618") as mock_transport:
+    with patch("toolbox_core.client.McpHttpTransportV20251125") as mock_transport:
         with warnings.catch_warnings(record=True) as w:
             warnings.simplefilter("always")
 
diff --git a/packages/toolbox-core/tests/test_e2e_mcp.py b/packages/toolbox-core/tests/test_e2e_mcp.py
index c35695ffa..7ffb3ddfa 100644
--- a/packages/toolbox-core/tests/test_e2e_mcp.py
+++ b/packages/toolbox-core/tests/test_e2e_mcp.py
@@ -24,11 +24,9 @@
 from toolbox_core.tool import ToolboxTool
 
 
-# TODO: Include draft versions in E2E integration tests once the server
-# supports SEP-2575 (stateless MCP / Request-Metadata).
 @pytest_asyncio.fixture(
     scope="function",
-    params=[v for v in Protocol.get_supported_mcp_versions() if "DRAFT" not in v],
+    params=[v for v in Protocol.get_supported_mcp_versions()],
 )
 async def toolbox(request):
     """Creates a ToolboxClient instance shared by all tests in this module."""
@@ -100,20 +98,27 @@ async def test_run_tool_missing_params(self, get_n_rows_tool: ToolboxTool):
         with pytest.raises(TypeError, match="missing a required argument: 'num_rows'"):
             await get_n_rows_tool()
 
-    async def test_protocol_fallback_e2e(self):
-        """Tests that a client using MCP_LATEST can fallback to an older protocol against a server that doesn't support the latest version."""
-        # The E2E server currently does not support DRAFT 2026, so this will trigger a fallback.
+    async def test_protocol_fallback_e2e(self, toolbox_server_url: str):
+        """Tests that a client using MCP_DRAFT can fallback to an older protocol against a server that doesn't support the draft version."""
+        # The E2E server currently does not support DRAFT 2026 on port 5000, so this will trigger a fallback.
+        # However, port 5001 does support DRAFT 2026.
         async with ToolboxClient(
-            "http://localhost:5000", protocol=Protocol.MCP_LATEST
+            toolbox_server_url, protocol=Protocol.MCP_DRAFT
         ) as client:
             tool = await client.load_tool("get-n-rows")
             response = await tool(num_rows="1")
             assert "row1" in response
             # Verify that fallback occurred by checking the transport's final protocol version
-            assert (
-                client._ToolboxClient__transport._protocol_version
-                != Protocol.MCP_LATEST.value
-            )
+            if "5001" in toolbox_server_url:
+                assert (
+                    client._ToolboxClient__transport._protocol_version
+                    == Protocol.MCP_DRAFT.value
+                )
+            else:
+                assert (
+                    client._ToolboxClient__transport._protocol_version
+                    != Protocol.MCP_DRAFT.value
+                )
 
     async def test_run_tool_wrong_param_type(self, get_n_rows_tool: ToolboxTool):
         """Invoke a tool with wrong param type."""
@@ -463,3 +468,25 @@ async def test_run_tool_with_wrong_map_value_type(self, toolbox: ToolboxClient):
                 execution_context={"env": "staging"},
                 user_scores={"user4": "not-an-integer"},
             )
+
+
+@pytest.mark.asyncio
+@pytest.mark.usefixtures("toolbox_server")
+async def test_mcp_default_protocol():
+    """Verify that omitting the protocol argument defaults correctly and works."""
+    async with ToolboxClient("http://localhost:5000") as client:
+        tool = await client.load_tool("get-n-rows")
+        response = await tool(num_rows="1")
+        assert "row1" in response
+
+
+@pytest.mark.asyncio
+@pytest.mark.usefixtures("toolbox_server")
+async def test_mcp_draft_fallback():
+    """Verify that explicitly using MCP_DRAFT against a server that doesn't support it falls back successfully."""
+    async with ToolboxClient(
+        "http://localhost:5000", protocol=Protocol.MCP_DRAFT
+    ) as client:
+        tool = await client.load_tool("get-n-rows")
+        response = await tool(num_rows="1")
+        assert "row1" in response
diff --git a/packages/toolbox-langchain/integration.cloudbuild.yaml b/packages/toolbox-langchain/integration.cloudbuild.yaml
index 140803960..ccadbb557 100644
--- a/packages/toolbox-langchain/integration.cloudbuild.yaml
+++ b/packages/toolbox-langchain/integration.cloudbuild.yaml
@@ -49,5 +49,5 @@ options:
   logging: CLOUD_LOGGING_ONLY
 substitutions:
   _VERSION: '3.13'
-  _TOOLBOX_VERSION: '1.4.0'
+  _TOOLBOX_VERSION: 'v1.6.0'
   _TOOLBOX_MANIFEST_VERSION: '34'
diff --git a/packages/toolbox-langchain/pyproject.toml b/packages/toolbox-langchain/pyproject.toml
index 247fdbfab..d8778d62d 100644
--- a/packages/toolbox-langchain/pyproject.toml
+++ b/packages/toolbox-langchain/pyproject.toml
@@ -50,6 +50,7 @@ test = [
     "pytest-asyncio==1.4.0",
     "pytest==9.0.3",
     "pytest-cov==7.1.0",
+    "numpy<2.2.0",
     "Pillow==12.2.0; python_version >= '3.10'",
     "google-cloud-secret-manager==2.28.0",
     "google-cloud-storage==3.10.1",
diff --git a/packages/toolbox-langchain/tests/conftest.py b/packages/toolbox-langchain/tests/conftest.py
index a1c87a7d8..7fe322b6d 100644
--- a/packages/toolbox-langchain/tests/conftest.py
+++ b/packages/toolbox-langchain/tests/conftest.py
@@ -25,7 +25,7 @@
 from typing import Generator
 
 import google
-import pytest_asyncio
+import pytest
 from google.auth import compute_engine
 from google.cloud import secretmanager, storage
 
@@ -75,7 +75,8 @@ def get_toolbox_binary_url(toolbox_version: str) -> str:
     arch = (
         "arm64" if os_system == "darwin" and platform.machine() == "arm64" else "amd64"
     )
-    return f"v{toolbox_version}/{os_system}/{arch}/toolbox"
+    ext = ".exe" if os_system == "windows" else ""
+    return f"{toolbox_version}/{os_system}/{arch}/toolbox{ext}"
 
 
 def get_auth_token(client_id: str) -> str:
@@ -92,17 +93,17 @@ def get_auth_token(client_id: str) -> str:
 
 
 #### Define Fixtures
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def project_id() -> str:
     return get_env_var("GOOGLE_CLOUD_PROJECT")
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def toolbox_version() -> str:
     return get_env_var("TOOLBOX_VERSION")
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def tools_file_path(project_id: str) -> Generator[str]:
     """Provides a temporary file path containing the tools manifest."""
     tools_manifest = access_secret_version(
@@ -115,7 +116,7 @@ def tools_file_path(project_id: str) -> Generator[str]:
     os.remove(tools_file_path)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def auth_token1(project_id: str) -> str:
     client_id = access_secret_version(
         project_id=project_id, secret_id="sdk_testing_client1"
@@ -123,7 +124,7 @@ def auth_token1(project_id: str) -> str:
     return get_auth_token(client_id)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def auth_token2(project_id: str) -> str:
     client_id = access_secret_version(
         project_id=project_id, secret_id="sdk_testing_client2"
@@ -131,32 +132,47 @@ def auth_token2(project_id: str) -> str:
     return get_auth_token(client_id)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None]:
     """Starts the toolbox server as a subprocess."""
     print("Downloading toolbox binary from gcs bucket...")
     source_blob_name = get_toolbox_binary_url(toolbox_version)
-    download_blob("mcp-toolbox-for-databases", source_blob_name, "toolbox")
+    bucket_name = (
+        "mcp-toolbox-for-databases-dev"
+        if toolbox_version in ("main", "mcp-v202606")
+        else "mcp-toolbox-for-databases"
+    )
+    download_blob(bucket_name, source_blob_name, "toolbox")
     print("Toolbox binary downloaded successfully.")
     try:
         print("Opening toolbox server process...")
         # Make toolbox executable
         os.chmod("toolbox", 0o700)
         # Run toolbox binary
-        toolbox_server = subprocess.Popen(
-            ["./toolbox", "--tools-file", tools_file_path]
+        toolbox_server_1 = subprocess.Popen(
+            ["./toolbox", "--port", "5000", "--tools-file", tools_file_path]
+        )
+        toolbox_server_2 = subprocess.Popen(
+            [
+                "./toolbox",
+                "--port",
+                "5001",
+                "--tools-file",
+                tools_file_path,
+                "--enable-draft-specs",
+            ]
         )
 
         # Wait for server to start
         # Retry logic with a timeout
         for _ in range(5):  # retries
-            time.sleep(2)
-            print("Checking if toolbox is successfully started...")
-            if toolbox_server.poll() is None:
-                print("Toolbox server started successfully.")
+            time.sleep(4)
+            print("Checking if both toolbox servers are successfully started...")
+            if toolbox_server_1.poll() is None and toolbox_server_2.poll() is None:
+                print("Toolbox servers started successfully.")
                 break
         else:
-            raise RuntimeError("Toolbox server failed to start after 5 retries.")
+            raise RuntimeError("Toolbox servers failed to start after 5 retries.")
     except subprocess.CalledProcessError as e:
         print(e.stderr.decode("utf-8"))
         print(e.stdout.decode("utf-8"))
@@ -164,5 +180,31 @@ def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None
     yield
 
     # Clean up toolbox server
-    toolbox_server.terminate()
-    toolbox_server.wait()
+    toolbox_server_1.terminate()
+    toolbox_server_2.terminate()
+    toolbox_server_1.wait()
+    toolbox_server_2.wait()
+
+
+@pytest.fixture(
+    params=["http://localhost:5000", "http://localhost:5001"], scope="session"
+)
+def toolbox_server_url(request) -> str:
+    return request.param
+
+
+@pytest.fixture(autouse=True)
+def patch_toolbox_client_url(toolbox_server_url):
+    from toolbox_core.client import ToolboxClient
+
+    original_init = ToolboxClient.__init__
+
+    def new_init(self, url="http://localhost:5000", *args, **kwargs):
+        if url == "http://localhost:5000":
+            url = toolbox_server_url
+        original_init(self, url, *args, **kwargs)
+
+    from unittest.mock import patch
+
+    with patch.object(ToolboxClient, "__init__", new_init, create=True):
+        yield
diff --git a/packages/toolbox-llamaindex/integration.cloudbuild.yaml b/packages/toolbox-llamaindex/integration.cloudbuild.yaml
index 028328fb7..2054900fa 100644
--- a/packages/toolbox-llamaindex/integration.cloudbuild.yaml
+++ b/packages/toolbox-llamaindex/integration.cloudbuild.yaml
@@ -49,5 +49,5 @@ options:
   logging: CLOUD_LOGGING_ONLY
 substitutions:
   _VERSION: '3.13'
-  _TOOLBOX_VERSION: '1.4.0'
+  _TOOLBOX_VERSION: 'v1.6.0'
   _TOOLBOX_MANIFEST_VERSION: '34'
diff --git a/packages/toolbox-llamaindex/pyproject.toml b/packages/toolbox-llamaindex/pyproject.toml
index ec8107ead..08b64b3d8 100644
--- a/packages/toolbox-llamaindex/pyproject.toml
+++ b/packages/toolbox-llamaindex/pyproject.toml
@@ -50,6 +50,7 @@ test = [
     "pytest-asyncio==1.4.0",
     "pytest==9.0.3",
     "pytest-cov==7.1.0",
+    "numpy<2.2.0",
     "Pillow==12.2.0; python_version >= '3.10'",
     "google-cloud-secret-manager==2.28.0",
     "google-cloud-storage==3.10.1",
diff --git a/packages/toolbox-llamaindex/tests/conftest.py b/packages/toolbox-llamaindex/tests/conftest.py
index c8a8fa5f9..e5bd6f771 100644
--- a/packages/toolbox-llamaindex/tests/conftest.py
+++ b/packages/toolbox-llamaindex/tests/conftest.py
@@ -25,7 +25,7 @@
 from typing import Generator
 
 import google
-import pytest_asyncio
+import pytest
 from google.auth import compute_engine
 from google.cloud import secretmanager, storage
 
@@ -75,7 +75,8 @@ def get_toolbox_binary_url(toolbox_version: str) -> str:
     arch = (
         "arm64" if os_system == "darwin" and platform.machine() == "arm64" else "amd64"
     )
-    return f"v{toolbox_version}/{os_system}/{arch}/toolbox"
+    ext = ".exe" if os_system == "windows" else ""
+    return f"{toolbox_version}/{os_system}/{arch}/toolbox{ext}"
 
 
 def get_auth_token(client_id: str) -> str:
@@ -92,17 +93,17 @@ def get_auth_token(client_id: str) -> str:
 
 
 #### Define Fixtures
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def project_id() -> str:
     return get_env_var("GOOGLE_CLOUD_PROJECT")
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def toolbox_version() -> str:
     return get_env_var("TOOLBOX_VERSION")
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def tools_file_path(project_id: str) -> Generator[str]:
     """Provides a temporary file path containing the tools manifest."""
     tools_manifest = access_secret_version(
@@ -115,7 +116,7 @@ def tools_file_path(project_id: str) -> Generator[str]:
     os.remove(tools_file_path)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def auth_token1(project_id: str) -> str:
     client_id = access_secret_version(
         project_id=project_id, secret_id="sdk_testing_client1"
@@ -123,7 +124,7 @@ def auth_token1(project_id: str) -> str:
     return get_auth_token(client_id)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def auth_token2(project_id: str) -> str:
     client_id = access_secret_version(
         project_id=project_id, secret_id="sdk_testing_client2"
@@ -131,32 +132,47 @@ def auth_token2(project_id: str) -> str:
     return get_auth_token(client_id)
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest.fixture(scope="session")
 def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None]:
     """Starts the toolbox server as a subprocess."""
     print("Downloading toolbox binary from gcs bucket...")
     source_blob_name = get_toolbox_binary_url(toolbox_version)
-    download_blob("mcp-toolbox-for-databases", source_blob_name, "toolbox")
+    bucket_name = (
+        "mcp-toolbox-for-databases-dev"
+        if toolbox_version in ("main", "mcp-v202606")
+        else "mcp-toolbox-for-databases"
+    )
+    download_blob(bucket_name, source_blob_name, "toolbox")
     print("Toolbox binary downloaded successfully.")
     try:
         print("Opening toolbox server process...")
         # Make toolbox executable
         os.chmod("toolbox", 0o700)
         # Run toolbox binary
-        toolbox_server = subprocess.Popen(
-            ["./toolbox", "--tools-file", tools_file_path]
+        toolbox_server_1 = subprocess.Popen(
+            ["./toolbox", "--port", "5000", "--tools-file", tools_file_path]
+        )
+        toolbox_server_2 = subprocess.Popen(
+            [
+                "./toolbox",
+                "--port",
+                "5001",
+                "--tools-file",
+                tools_file_path,
+                "--enable-draft-specs",
+            ]
         )
 
         # Wait for server to start
         # Retry logic with a timeout
         for _ in range(5):  # retries
             time.sleep(4)
-            print("Checking if toolbox is successfully started...")
-            if toolbox_server.poll() is None:
-                print("Toolbox server started successfully.")
+            print("Checking if both toolbox servers are successfully started...")
+            if toolbox_server_1.poll() is None and toolbox_server_2.poll() is None:
+                print("Toolbox servers started successfully.")
                 break
         else:
-            raise RuntimeError("Toolbox server failed to start after 5 retries.")
+            raise RuntimeError("Toolbox servers failed to start after 5 retries.")
     except subprocess.CalledProcessError as e:
         print(e.stderr.decode("utf-8"))
         print(e.stdout.decode("utf-8"))
@@ -164,5 +180,31 @@ def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None
     yield
 
     # Clean up toolbox server
-    toolbox_server.terminate()
-    toolbox_server.wait()
+    toolbox_server_1.terminate()
+    toolbox_server_2.terminate()
+    toolbox_server_1.wait()
+    toolbox_server_2.wait()
+
+
+@pytest.fixture(
+    params=["http://localhost:5000", "http://localhost:5001"], scope="session"
+)
+def toolbox_server_url(request) -> str:
+    return request.param
+
+
+@pytest.fixture(autouse=True)
+def patch_toolbox_client_url(toolbox_server_url):
+    from toolbox_core.client import ToolboxClient
+
+    original_init = ToolboxClient.__init__
+
+    def new_init(self, url="http://localhost:5000", *args, **kwargs):
+        if url == "http://localhost:5000":
+            url = toolbox_server_url
+        original_init(self, url, *args, **kwargs)
+
+    from unittest.mock import patch
+
+    with patch.object(ToolboxClient, "__init__", new_init, create=True):
+        yield