tengu_mcp_discovery_source
A Claude Code feature flag, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.
Startup no longer dials cached HTTP or SSE MCP servers; they restore from cache and connect on first use.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.221.
In the changelogs
4Releases whose published page names tengu_mcp_discovery_source.
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v2.1.268
MCP discovery can skip cache/connect when tools are already known
MCP server setup can now skip the discovery cache and connection entirely when a server's tools are already known
gate cited by this entry
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v2.1.221
MCP servers can start from a discovery cache and connect lazily
Startup no longer dials cached HTTP or SSE MCP servers; they restore from cache and connect on first use.
gate cited by this entry, found in this entry's text
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v2.1.221
MCP servers can start in a new "cached" state instead of blocking on connect
MCP servers with a saved cache now show tools instantly and only connect when you first use them.
gate cited by this entry, found in this entry's text
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v2.1.221
Discovery-cache misses are classified in telemetry
MCP tool discovery now logs whether the cache was used, and servers with skills or channels deliberately skip it.
gate cited by this entry, found in this entry's text
Gate readings
0No release here has a gate table behind it for this flag. Most published releases have none at all: the readings exist only for versions the pipeline captured flag state on.
First cited
1The earliest release whose published evidence quoted tengu_mcp_discovery_source was v2.1.221, 3 Aug 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.
Presence across releases
0The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was never mined.
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the feature flag does. All feature flags.