Nothing to try yetTier: how much it should matter to you
4Useful: my rating, 1 to 5
4Signal: worth watching, 1 to 5
MCPArea: what it touches
In DevelopmentKind: in v2.1.265,
What probably matters to youSection of the release
What
A new sdkMcpServerManifests field on set_servers lets the host application pre-run an MCP server's own initialize and tools/list calls in-process and hand the results directly to the CLI. The CLI then uses those results to answer its own MCP client's handshake locally, instead of exchanging mcp_message control messages back and forth before the first turn.
Why
Registering multiple in-process MCP servers this way costs no control-channel round trips before the first turn, which should make sessions with several SDK-provided MCP servers start faster.
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
What has happened since
Flag reading movedThe flag server now returns on for tengu_sdk_mcp_manifests, read as this account.A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading movedThe flag server now returns nothing at all, having stopped carrying it for tengu_sdk_mcp_manifests, read as this account.A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
