Rename FastMCP to MCPServer (#1951)

src/mcp/client/_memory.py

@@ -10,7 +10,7 @@ import anyio
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 
 from mcp.server import Server
-from mcp.server.fastmcp import FastMCP
+from mcp.server.mcpserver import MCPServer
 from mcp.shared.memory import create_client_server_memory_streams
 from mcp.shared.message import SessionMessage
 
@@ -23,7 +23,7 @@ class InMemoryTransport:
     stopped when the context manager exits.
 
     Example:
-        server = FastMCP("test")
+        server = MCPServer("test")
         transport = InMemoryTransport(server)
 
         async with transport.connect() as (read_stream, write_stream):
@@ -36,11 +36,11 @@ class InMemoryTransport:
             result = await client.call_tool("my_tool", {...})
     """
 
-    def __init__(self, server: Server[Any] | FastMCP, *, raise_exceptions: bool = False) -> None:
+    def __init__(self, server: Server[Any] | MCPServer, *, raise_exceptions: bool = False) -> None:
         """Initialize the in-memory transport.
 
         Args:
-            server: The MCP server to connect to (Server or FastMCP instance)
+            server: The MCP server to connect to (Server or MCPServer instance)
             raise_exceptions: Whether to raise exceptions from the server
         """
         self._server = server
@@ -61,10 +61,10 @@ class InMemoryTransport:
         Yields:
             A tuple of (read_stream, write_stream) for bidirectional communication
         """
-        # Unwrap FastMCP to get underlying Server
+        # Unwrap MCPServer to get underlying Server
         actual_server: Server[Any]
-        if isinstance(self._server, FastMCP):
-            actual_server = self._server._mcp_server  # type: ignore[reportPrivateUsage]
+        if isinstance(self._server, MCPServer):
+            actual_server = self._server._lowlevel_server  # type: ignore[reportPrivateUsage]
         else:
             actual_server = self._server
 

src/mcp/client/client.py

@@ -8,7 +8,7 @@ from typing import Any
 from mcp.client._memory import InMemoryTransport
 from mcp.client.session import ClientSession, ElicitationFnT, ListRootsFnT, LoggingFnT, MessageHandlerFnT, SamplingFnT
 from mcp.server import Server
-from mcp.server.fastmcp import FastMCP
+from mcp.server.mcpserver import MCPServer
 from mcp.shared.session import ProgressFnT
 from mcp.types import (
     CallToolResult,
@@ -34,14 +34,14 @@ class Client:
     """A high-level MCP client for connecting to MCP servers.
 
     Currently supports in-memory transport for testing. Pass a Server or
-    FastMCP instance directly to the constructor.
+    MCPServer instance directly to the constructor.
 
     Example:
         ```python
         from mcp.client import Client
-        from mcp.server.fastmcp import FastMCP
+        from mcp.server.mcpserver import MCPServer
 
-        server = FastMCP("test")
+        server = MCPServer("test")
 
         @server.tool()
         def add(a: int, b: int) -> int:
@@ -55,7 +55,7 @@ class Client:
         ```
     """
 
-    # TODO(felixweinberger): Expand to support all transport types (like FastMCP 2):
+    # TODO(felixweinberger): Expand to support all transport types:
     # - Add ClientTransport base class with connect_session() method
     # - Add StreamableHttpTransport, SSETransport, StdioTransport
     # - Add infer_transport() to auto-detect transport from input type
@@ -64,7 +64,7 @@ class Client:
 
     def __init__(
         self,
-        server: Server[Any] | FastMCP,
+        server: Server[Any] | MCPServer,
         *,
         # TODO(Marcelo): When do `raise_exceptions=True` actually raises?
         raise_exceptions: bool = False,
@@ -79,7 +79,7 @@ class Client:
         """Initialize the client with a server.
 
         Args:
-            server: The MCP server to connect to (Server or FastMCP instance)
+            server: The MCP server to connect to (Server or MCPServer instance)
             raise_exceptions: Whether to raise exceptions from the server
             read_timeout_seconds: Timeout for read operations
             sampling_callback: Callback for handling sampling requests

src/mcp/client/session_group.py

@@ -15,7 +15,7 @@ from typing import Any, TypeAlias
 
 import anyio
 import httpx
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from typing_extensions import Self
 
 import mcp
@@ -103,9 +103,9 @@ class ClientSessionGroup:
     class _ComponentNames(BaseModel):
         """Used for reverse index to find components."""
 
-        prompts: set[str] = set()
-        resources: set[str] = set()
-        tools: set[str] = set()
+        prompts: set[str] = Field(default_factory=set)
+        resources: set[str] = Field(default_factory=set)
+        tools: set[str] = Field(default_factory=set)
 
     # Standard MCP components.
     _prompts: dict[str, types.Prompt]