tengu_headless_mcp_prewait
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.
Waiting for MCP servers before a headless run is tidied up and logs more detail.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.221.
In the changelogs
5Releases whose published page names tengu_headless_mcp_prewait.
-
v2.1.288
Headless startup can skip waiting for MCP servers the conversation doesn't need
Non-interactive sessions can now start without waiting for local MCP servers whose tools are all deferred
found in this entry's text
-
v2.1.281
Remote sessions can defer connecting MCP servers set via set_servers
Remote sessions can defer connecting MCP servers added via set_servers, with turns waiting up to 8 seconds for them
found in this entry's text
-
v2.1.265
Headless MCP prewait can now wait for specific remote MCP servers by name, not just local-only
Headless MCP startup wait can now target specific named remote servers, not just local ones
gate cited by this entry, found in this entry's text
-
v2.1.221
Headless MCP pre-wait takes an options object and reports more telemetry
Waiting for MCP servers before a headless run is tidied up and logs more detail.
gate cited by this entry, found in this entry's text
-
v2.1.221
Telemetry values are validated before being sent
Unexpected telemetry values are replaced with a placeholder instead of being sent raw.
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_headless_mcp_prewait 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.