tengu_mcp_protocol_negotiation_http
A Claude Code feature flag, read out of the shipped bundle. It has been in the build since v2.1.221, including the newest one read.
A newer MCP protocol handshake exists per transport but every gate falls back to legacy here.
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_protocol_negotiation_http.
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v2.1.295
claude.ai connectors now use automatic MCP protocol negotiation by default
MCP servers reached through claude.ai connectors now agree a protocol version automatically unless the server explicitly turns this off
gate cited by this entry
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v2.1.274
MCP HTTP protocol negotiation default flips to enabled via tengu_mcp_protocol_negotiation_http
MCP HTTP servers now default to attempting protocol version auto-negotiation instead of legacy mode
named in this entry, gate cited by this entry, found in this entry's text
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v2.1.274
tengu_mcp_protocol_negotiation_http fallback flips from legacy to auto-negotiate
MCP servers connected over HTTP now default to trying the newer protocol handshake instead of legacy mode
named in this entry, gate cited by this entry, found in this entry's text
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v2.1.221
MCP protocol-era negotiation (2026-07-28 "modern" revision) added behind per-transport gates
A newer MCP protocol handshake exists per transport but every gate falls back to legacy here.
gate cited by this entry, found in this entry's text
Gate readings
3| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.295 read on another version | On for this account, and not off by default | on | on | on |
| v2.1.274 read on another version | On for this account, and not off by default | on | on | on |
| v2.1.221 read on another version | Off by default, switched on for this account | on | on | off |
Two arms, because they disagree: this account is the one account this site reads and anonymous is a baseline with no identity attached. A reading says nothing about your account, and off cannot rule out a rollout both readings sit outside of. What these readings can and cannot show.
Flag server, over time
21| Read as | Reading | From | Until | Version installed |
|---|---|---|---|---|
| anonymous | on | 2026-10-17T05:30:04Z | 2026-10-22T10:55:04Z | v2.1.302 to v2.1.308 |
| this account | on | 2026-10-07T18:00:12Z | 2026-10-22T10:55:04Z | v2.1.292 to v2.1.308 |
| anonymous | no longer carried | 2026-10-17T05:25:57Z | 2026-10-17T05:25:57Z | v2.1.302 |
| anonymous | on | 2026-08-19T04:25:04Z | 2026-10-17T05:10:04Z | v2.1.233 to v2.1.302 |
| this account | off | 2026-10-07T17:59:34Z | 2026-10-07T17:59:34Z | v2.1.293 |
| this account | on | 2026-09-10T21:47:12Z | 2026-10-07T17:10:05Z | v2.1.268 to v2.1.292 |
| this account | no longer carried | 2026-09-10T21:46:45Z | 2026-09-10T21:46:45Z | v2.1.268 |
| this account | on | 2026-09-08T20:36:15Z | 2026-09-10T17:40:05Z | v2.1.263 to v2.1.267 |
| this account | no longer carried | 2026-09-08T20:34:58Z | 2026-09-08T20:34:58Z | v2.1.265 |
| this account | on | 2026-09-06T02:40:05Z | 2026-09-08T18:45:05Z | v2.1.261 to v2.1.263 |
| this account | no longer carried | 2026-09-06T02:36:19Z | 2026-09-06T02:36:19Z | v2.1.263 |
| this account | on | 2026-08-22T13:25:05Z | 2026-09-06T01:55:04Z | v2.1.233 to v2.1.261 |
| this account | off | 2026-08-22T13:25:01Z | 2026-08-22T13:25:01Z | v2.1.240 |
| this account | on | 2026-08-20T07:25:04Z | 2026-08-22T12:15:05Z | v2.1.233 |
| this account | off | 2026-08-20T06:30:05Z | 2026-08-20T06:30:05Z | v2.1.233 |
| this account | on | 2026-08-18T18:55:06Z | 2026-08-20T06:10:06Z | v2.1.233 |
| anonymous | no longer carried | 2026-08-19T04:20:14Z | 2026-08-19T04:20:14Z | v2.1.233 |
| anonymous | on | 2026-08-18T13:15:04Z | 2026-08-19T03:45:04Z | v2.1.233 |
| this account | off | 2026-08-18T18:50:25Z | 2026-08-18T18:50:25Z | v2.1.235 |
| this account | on | 2026-08-14T22:10:05Z | 2026-08-18T17:30:05Z | v2.1.232 to v2.1.233 |
| anonymous | off | 2026-08-14T22:10:05Z | 2026-08-18T11:25:04Z | v2.1.232 to v2.1.233 |
One row per unbroken stretch of one reading, newest first, from snapshots taken every twenty-five minutes or so. No longer carried is not off: it means the flag server stopped returning the gate at all, which is what a retired experiment looks like. The version column is what was installed when the reading was taken, not what caused it.
First cited
2The earliest release whose published evidence quoted tengu_mcp_protocol_negotiation_http 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
1Build by build
76One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.
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.