Add version parameter to FastMCP constructor

src/fastmcp/server/server.py

@@ -110,6 +110,7 @@ class FastMCP(Generic[LifespanResultT]):
     def __init__(
         self,
         name: str | None = None,
+        version: str | None = None,
         instructions: str | None = None,
         auth: OAuthProvider | None = None,
         lifespan: (
@@ -175,6 +176,7 @@ class FastMCP(Generic[LifespanResultT]):
             self._has_lifespan = True
         self._mcp_server = MCPServer[LifespanResultT](
             name=name or "FastMCP",
+            version=version,
             instructions=instructions,
             lifespan=_lifespan_wrapper(self, lifespan),
         )

tests/client/test_client.py

@@ -321,6 +321,29 @@ async def test_initialize_result_disconnected(fastmcp_server):
         _ = client.initialize_result
 
 
+async def test_server_info_custom_version():
+    """Test that custom version is properly set in serverInfo."""
+    # Test with custom version
+    server_with_version = FastMCP("CustomVersionServer", version="1.2.3")
+    client = Client(transport=FastMCPTransport(server_with_version))
+
+    async with client:
+        result = client.initialize_result
+        assert result.serverInfo.name == "CustomVersionServer"
+        assert result.serverInfo.version == "1.2.3"
+
+    # Test without version (backward compatibility)
+    server_without_version = FastMCP("DefaultVersionServer")
+    client = Client(transport=FastMCPTransport(server_without_version))
+
+    async with client:
+        result = client.initialize_result
+        assert result.serverInfo.name == "DefaultVersionServer"
+        # Should fall back to MCP library version
+        assert result.serverInfo.version is not None
+        assert result.serverInfo.version != "1.2.3"  # Should be different from custom version
+
+
 async def test_client_nested_context_manager(fastmcp_server):
     """Test that the client connects and disconnects once in nested context manager."""