Source Intelligence

DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

All of v2.1.221 Home All releases olderv2.1.220 v2.1.222newer

Discovery-cache misses are classified in telemetry

Under the hood
Useful2 Signal0
MCP

MCP tool discovery now logs whether the cache was used, and servers with skills or channels deliberately skip it.

Feature flag
tengu_mcp_discovery_cache 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 v2.1.221: off

These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.

Read once, for one account on one subscription tier, against v2.1.221. It isn't a statement about your account. What a flag value here can and cannot tell you

What

A new event records where a server's tools came from, distinguishing real cache misses from deliberate bypasses.

Details
  • tengu_mcp_discovery_source reports cache_fresh or cache_stale for hits, and a normalized reason otherwise.
  • Reasons meaning "we connected anyway" collapse to live.
  • Genuine misses report miss_disabled, miss_expired, miss_corrupt, miss_strike or miss_no_fingerprint.
  • Two mapped reasons are new opt-outs: skills-capable and channel-capable servers deliberately bypass the cache.
  • Gated on tengu_mcp_discovery_cache, which falls back to enabled.
Evidence

miss_no_fingerprint

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.221 →