tengu_mcp_protocol_negotiation_ccr
A Claude Code feature flag, read out of the shipped bundle. It has been in the build since v2.1.236, including the newest one read.
The ccr-proxy MCP transport can negotiate protocol versions, but stays on legacy unless a flag is turned on.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.236.
In the changelogs
3Releases whose published page names tengu_mcp_protocol_negotiation_ccr.
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v2.1.299
MCP error code -32021 now handled with -32003 and -32601
Claude Code now treats the MCP error code -32021 the same way as -32003 and -32601 in one of its error checks
gate cited by this entry
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v2.1.299
MCP requests record whether the main handler answered or stood aside
MCP requests now try a main handler, fall back to a second one if it gives nothing, and record which happened
gate cited by this entry, found in this entry's text
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v2.1.236
MCP protocol auto-negotiation now covers the ccr-proxy transport, off by default
The ccr-proxy MCP transport can negotiate protocol versions, but stays on legacy unless a flag is turned on.
gate cited by this entry, found in this entry's text
Gate readings
2| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.299 read on another version | On for this account, and not off by default | on | on | on |
| v2.1.236 | Not enough to say | no value returned | no value returned | 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
12| Read as | Reading | From | Until | Version installed |
|---|---|---|---|---|
| anonymous | on | 2026-10-17T05:30:04Z | 2026-10-22T06:25:04Z | v2.1.302 to v2.1.308 |
| this account | on | 2026-09-10T21:47:12Z | 2026-10-22T06:25:04Z | v2.1.268 to v2.1.308 |
| anonymous | no longer carried | 2026-10-17T05:25:57Z | 2026-10-17T05:25:57Z | v2.1.302 |
| anonymous | on | 2026-09-02T10:35:04Z | 2026-10-17T05:10:04Z | v2.1.257 to v2.1.302 |
| 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 | 2026-09-02T11:25:05Z | 2026-09-06T01:55:04Z | v2.1.257 to v2.1.261 |
| this account | off | 2026-08-20T16:55:04Z | 2026-09-02T10:35:04Z | v2.1.233 to v2.1.257 |
| anonymous | off | 2026-08-20T16:25:06Z | 2026-09-02T10:05:06Z | v2.1.233 to v2.1.257 |
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
1The earliest release whose published evidence quoted tengu_mcp_protocol_negotiation_ccr was v2.1.236, 19 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
62One 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.