Nothing to try yetTier: how much it should matter to you
3Useful: my rating, 1 to 5
3Signal: worth watching, 1 to 5
MCPArea: what it touches
In DevelopmentKind: in v2.1.265,
In DevelopmentSection of the release
What
The initialize control request now accepts sdkMcpServerManifests: a pre-captured "host manifest" (an initializeResult plus an optional toolsListResult) for SDK-backed MCP servers. When present, Claude Code validates it against the required MCP protocol version and replays it instead of performing the usual live control-channel handshake for that server.
If a manifest is malformed, uses a mismatched protocol version, or contains paginated tool results it can't replay, Claude Code logs and reports this via telemetry (mcp_sdk_manifest_invalid_initialize, _invalid_tools_list, _paginated_tools_list, _replay_failed) and falls back to the normal handshake instead of applying the bad manifest.
Why
Replaying a known-good manifest avoids the cost and round-trip of a live handshake for SDK MCP servers, while the validation and fallback keep things working correctly if the supplied manifest is bad or incomplete.
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed sinceAnthropic's documentation has since written up sdkMcpServerManifests, on Agent SDK reference - TypeScript.The request's `sdkMcpServerManifests` field and the response's `sdk_mcp_manifests_parked` field are for the in-process [SDK MCP servers](/docs/en/agent-sdk/custom-tools) you created with [`createSdkMcpServer()`](#createsdkmcpserver). Your …agent-sdk/typescriptsee the edit
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agreesAnthropic's documentation has since written up sdkMcpServerManifests, on Agent SDK reference - TypeScript.
