Fix task capabilities location (issue #2870)

Tasks belong in capabilities.tasks (first-class field) per SEP-1686,
not capabilities.experimental.tasks. This fixes VS Code Copilot 1.107+
integration which checks capabilities.tasks?.requests?.tools?.call.

Changes:
- Update get_task_capabilities() to return ServerTasksCapability types
- Override get_capabilities() in LowLevelServer to set tasks field
- Remove experimental_capabilities parameter usage
- Update test to verify correct location

Fixes #2870

src/fastmcp/client/transports.py

@@ -36,7 +36,6 @@ from fastmcp.client.auth.oauth import OAuth
 from fastmcp.mcp_config import MCPConfig, infer_transport_type_from_url
 from fastmcp.server.dependencies import get_http_headers
 from fastmcp.server.server import FastMCP
-from fastmcp.server.tasks.capabilities import get_task_capabilities
 from fastmcp.utilities.logging import get_logger
 from fastmcp.utilities.mcp_server_config.v1.environments.uv import UVEnvironment
 
@@ -900,16 +899,11 @@ class FastMCPTransport(ClientTransport):
                 anyio.create_task_group() as tg,
                 _enter_server_lifespan(server=self.server),
             ):
-                # Build experimental capabilities
-                experimental_capabilities = get_task_capabilities()
-
                 tg.start_soon(
                     lambda: self.server._mcp_server.run(
                         server_read,
                         server_write,
-                        self.server._mcp_server.create_initialization_options(
-                            experimental_capabilities=experimental_capabilities
-                        ),
+                        self.server._mcp_server.create_initialization_options(),
                         raise_exceptions=self.raise_exceptions,
                     )
                 )

src/fastmcp/server/http.py

@@ -21,7 +21,6 @@ from starlette.types import Lifespan, Receive, Scope, Send
 
 from fastmcp.server.auth import AuthProvider
 from fastmcp.server.auth.middleware import RequireAuthMiddleware
-from fastmcp.server.tasks.capabilities import get_task_capabilities
 from fastmcp.utilities.logging import get_logger
 
 if TYPE_CHECKING:
@@ -160,15 +159,10 @@ def create_sse_app(
     # Create handler for SSE connections
     async def handle_sse(scope: Scope, receive: Receive, send: Send) -> Response:
         async with sse.connect_sse(scope, receive, send) as streams:
-            # Build experimental capabilities
-            experimental_capabilities = get_task_capabilities()
-
             await server._mcp_server.run(
                 streams[0],
                 streams[1],
-                server._mcp_server.create_initialization_options(
-                    experimental_capabilities=experimental_capabilities
-                ),
+                server._mcp_server.create_initialization_options(),
             )
         return Response()
 

src/fastmcp/server/low_level.py

@@ -163,6 +163,31 @@ class LowLevelServer(_Server[LifespanResultT, RequestT]):
             **kwargs,
         )
 
+    def get_capabilities(
+        self,
+        notification_options: NotificationOptions,
+        experimental_capabilities: dict[str, dict[str, Any]],
+    ) -> mcp.types.ServerCapabilities:
+        """Override to set capabilities.tasks as a first-class field per SEP-1686.
+
+        This ensures task capabilities appear in capabilities.tasks instead of
+        capabilities.experimental.tasks, which is required by the MCP spec and
+        enables proper task detection by clients like VS Code Copilot 1.107+.
+        """
+        from fastmcp.server.tasks.capabilities import get_task_capabilities
+
+        # Get base capabilities from SDK (pass empty dict for experimental)
+        # since we'll set tasks as a first-class field instead
+        capabilities = super().get_capabilities(
+            notification_options,
+            experimental_capabilities or {},
+        )
+
+        # Set tasks as a first-class field (not experimental) per SEP-1686
+        capabilities.tasks = get_task_capabilities()
+
+        return capabilities
+
     async def run(
         self,
         read_stream: MemoryObjectReceiveStream[SessionMessage | Exception],

src/fastmcp/server/server.py

@@ -75,7 +75,6 @@ from fastmcp.server.http import (
 )
 from fastmcp.server.low_level import LowLevelServer
 from fastmcp.server.middleware import Middleware, MiddlewareContext
-from fastmcp.server.tasks.capabilities import get_task_capabilities
 from fastmcp.server.tasks.config import TaskConfig
 from fastmcp.server.tasks.handlers import (
     handle_prompt_as_task,
@@ -2508,9 +2507,6 @@ class FastMCP(Generic[LifespanResultT]):
                         f"Starting MCP server {self.name!r} with transport 'stdio'"
                     )
 
-                    # Build experimental capabilities
-                    experimental_capabilities = get_task_capabilities()
-
                     await self._mcp_server.run(
                         read_stream,
                         write_stream,
@@ -2518,7 +2514,6 @@ class FastMCP(Generic[LifespanResultT]):
                             notification_options=NotificationOptions(
                                 tools_changed=True
                             ),
-                            experimental_capabilities=experimental_capabilities,
                         ),
                     )
 

src/fastmcp/server/tasks/capabilities.py

@@ -1,22 +1,29 @@
 """SEP-1686 task capabilities declaration."""
 
-from typing import Any
+from mcp.types import (
+    ServerTasksCapability,
+    ServerTasksRequestsCapability,
+    TasksCancelCapability,
+    TasksListCapability,
+    TasksToolsCapability,
+)
 
 
-def get_task_capabilities() -> dict[str, Any]:
-    """Return the SEP-1686 task capabilities structure.
+def get_task_capabilities() -> ServerTasksCapability:
+    """Return the SEP-1686 task capabilities.
 
-    This is the standard capabilities map advertised to clients,
-    declaring support for list, cancel, and request operations.
+    Returns task capabilities as a first-class ServerCapabilities field,
+    declaring support for list, cancel, and request operations per SEP-1686.
+
+    Note: prompts/resources are passed via extra_data since the SDK types
+    don't include them yet (FastMCP supports them ahead of the spec).
     """
-    return {
-        "tasks": {
-            "list": {},
-            "cancel": {},
-            "requests": {
-                "tools": {"call": {}},
-                "prompts": {"get": {}},
-                "resources": {"read": {}},
-            },
-        }
-    }
+    return ServerTasksCapability(
+        list=TasksListCapability(),
+        cancel=TasksCancelCapability(),
+        requests=ServerTasksRequestsCapability(
+            tools=TasksToolsCapability(call={}),
+            prompts={"get": {}},
+            resources={"read": {}},
+        ),
+    )

tests/server/tasks/test_task_capabilities.py

@@ -11,7 +11,7 @@ from fastmcp.server.tasks import get_task_capabilities
 
 
 async def test_capabilities_include_tasks():
-    """Server capabilities always include tasks."""
+    """Server capabilities always include tasks in first-class field (SEP-1686)."""
     mcp = FastMCP("capability-test")
 
     @mcp.tool()
@@ -22,11 +22,11 @@ async def test_capabilities_include_tasks():
         # Get server initialization result which includes capabilities
         init_result = client.initialize_result
 
-        # Verify tasks capability is present
-        assert init_result.capabilities.experimental is not None
-        assert "tasks" in init_result.capabilities.experimental
-        tasks_cap = init_result.capabilities.experimental["tasks"]
-        assert tasks_cap == get_task_capabilities()["tasks"]
+        # Verify tasks capability is present as a first-class field (not experimental)
+        assert init_result.capabilities.tasks is not None
+        assert init_result.capabilities.tasks == get_task_capabilities()
+        # Verify it's NOT in experimental
+        assert "tasks" not in (init_result.capabilities.experimental or {})
 
 
 async def test_client_uses_task_capable_session():