{"version":"2.1.311","anchor":"tools-used-header-gated-by-tengu-snug-mitten","canonical_anchor":"tools-used-header-gated-by-tengu-snug-mitten","heading":"API requests can carry a list of the tools in use, and more request bodies are compressed","tier":"soon","area":"API Requests","scope":"individual","heads_up":false,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.311\/e\/tools-used-header-gated-by-tengu-snug-mitten","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.311","markdown":"### API requests can carry a list of the tools in use, and more request bodies are compressed\n\nRequests to Anthropic may carry an `x-claude-code-sandy-plover` header listing the tools used, and gzip now covers non-string request bodies\n\n**What**\n\nRequests that Claude Code sends to Anthropic's API (the service that runs the model) may now carry a header (an extra labelled line sent with a request) that lists the tools the session uses.\n\n- The header is named `x-claude-code-sandy-plover` and is only attached for first-party addresses, meaning Anthropic's own API.\n\n- The list of tool names is capped at 7168 bytes. Common tools are placed last, and `incomplete_list` is reported when names had to be left out.\n\n- Whether the header is sent depends on a feature flag, `tengu_snug_mitten`, plus one other check. Nothing has been read about the state of that flag.\n\nThe same release also changes how requests are sent:\n\n- Request bodies that are not plain text are now gzipped (compressed) too, using a helper that can handle streamed data. Before, only plain-text bodies were compressed. Extra size details about each body are now recorded.\n\n- When estimating the token count of tool calls (a token is a small chunk of text the model reads), Claude Code now remembers the length of each call's input instead of measuring it again.\n\n**Why**\n\nThis changes what is sent with each API request. When the header is in use, Anthropic can see which tools a session uses.\n\n- Flag `tengu_snug_mitten`: Not enough to say (read for one account on one subscription tier against v2.1.311; this account: no value returned, anonymous baseline: no value returned, compiled default: off) These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.\n- Area: API Requests\n- Tier: Nothing to try yet\n- Useful: 2\/5\n- Signal: 3\/5\n- Scope: individual\n- Heads-up: no\n- Present in the build but not switched on"}