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Sweep 28 Aug 2026 · 00:00Z Build v2.1.250 478 read Stable v2.1.236 Latest v2.1.250 Next v2.1.250 Feeds RSS JSON llms.txt

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.

Reference / Environment variables

MCP_PROTOCOL_NEGOTIATION

A Claude Code environment variable, read out of the shipped bundle. It has been in the build since v2.1.221, including the newest one read.

What it is

In auto mode MCP connections would probe for a modern protocol and fall back to legacy, but nothing enables it.

Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.221.

Presence across releases

ReleasesReadingDeclared typeDefault
2.1.245 – 2.1.250 5 releases never mined — —
2.1.221 – 2.1.243 22 releases in the build str —

A row reading never mined is a release with no archived bundle behind it. Nothing was read out of it, so nothing here says whether the name was in it. A declared type or a default is only ever what that release's own bundle stated.

Changelog entries naming it

  1. v2.1.221New MCP protocol-era negotiation with probe and legacy fallback

    In auto mode MCP connections would probe for a modern protocol and fall back to legacy, but nothing enables it.

    named in this entry

Documentation pages

A reference table page is one whose own table defines this name, and it is where the description above came from. A page that mentions it carries the name somewhere in its text and may say nothing about it at all. Every page carrying it.

Names beside it

Every environment variable in the inventory starting mcp, up to twelve of them.

MCP_CLIENT_SECRETNo description from anybody. 2.1.138 MCP_CONNECT_TIMEOUT_MSVery large MCP_TIMEOUT values are capped instead of overflowing and timing out instantly. 2.1.138 MCP_CONNECTION_NONBLOCKINGFive more environment variables, including stream and byte watchdogs, can be set in settings.json. 2.1.138 MCP_DISCOVERY_CACHEStartup no longer dials cached HTTP or SSE MCP servers; they restore from cache and connect on first use. 2.1.217 MCP_DISCOVERY_CACHE_MAX_STALE_SNo description from anybody. 2.1.217 MCP_DISCOVERY_CACHE_STRIKESNo description from anybody. 2.1.238 MCP_DISCOVERY_CACHE_TTL_SNo description from anybody. 2.1.217 MCP_OAUTH_CALLBACK_PORTAbout 220 environment variables now parse and validate in one place, including bounds checks. 2.1.138 MCP_OAUTH_CLIENT_METADATA_URLNo description from anybody. 2.1.138 MCP_REMOTE_SERVER_CONNECTION_BATCH_SIZETwo new env vars set how many MCP servers connect at once, local and remote. 2.1.138 MCP_SDK_GENERATIONNo description from anybody. 2.1.218 MCP_SERVER_CONNECTION_BATCH_SIZEMCP servers now connect three at a time; set MCP_SERVER_CONNECTION_BATCH_SIZE to change it. 2.1.138

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 environment variable does. All environment variables.