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Sweep 22 Sep 2026 · 17:19Z Build v2.1.280 501 read Stable v2.1.267 Latest v2.1.280 Next v2.1.280 Feeds RSS JSON llms.txt Unofficial
Claude Code v2.1.265 ·

SDK MCP servers can now skip the control-channel handshake via manifests

SDK-registered in-process MCP servers can now skip a round-trip handshake at session start

TierNothing to try yethow much it should matter to you
Useful4my rating, 1 to 5
Signal4worth watching, 1 to 5
AreaMCPwhat it touches
KindIn Developmentin v2.1.265,
Nothing to try yet Notable No documentation found

SDK-registered in-process MCP servers can now skip a round-trip handshake at session start

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.

Read from
Names in the bundlesdkMcpServerManifests
Feature flag
tengu_sdk_mcp_manifests Not enough to say

Nothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.

This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.265: on

Read once, for one account on one subscription tier, against v2.1.265. It isn't a statement about your account. What a flag value here can and cannot tell you

What has happened since
Flag reading moved The 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 moved The 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.

See this across every release →

How sure we are
One source agreesOne thing we can check says the same as this entry.
The name it cites is new in this buildNew in this build: tengu_sdk_mcp_manifests

See this entry in the whole of v2.1.265 →

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