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Reading a new release v2.1.251 Analysing changes · 2/5 Sorting the findings · 1/4 steps 470 findings $18.91 so far

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.

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Request Body Gzip Compression [In Development]

Feature flag
tengu_gzip_request_bodies Not enough to say

Nothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.

This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.199: on

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.

Read once, for one account on one subscription tier, against v2.1.199. It isn't a statement about your account. What a flag value here can and cannot tell you

What

Gzip compression of API request bodies, reducing bandwidth for large context uploads.

Details
  • Controlled by yGd(): checks CLAUDE_CODE_GZIP_REQUEST_BODIES env var first; if unset, falls back to the tengu_gzip_request_bodies feature flag (default false)
  • Only applies to requests whose target host is api.anthropic.com (verified by wce() URL host check); Bedrock, Vertex, custom ANTHROPIC_BASE_URL, and any non-Anthropic endpoints are unaffected
  • When enabled, sets compress: "gzip" on the outgoing fetch options object, instructing the underlying HTTP layer to gzip-encode the request body before transmission
  • When the request body is a string, a random whitespace suffix is appended before compression: a newline (\n) followed by 0–256 randomly chosen space or tab characters; this adds entropy to the payload to improve compression ratio consistency across requests
  • No changes are made to response handling; response decompression was already in place
Status

Feature-flagged (tengu_gzip_request_bodies, defaulting false). Can be force-enabled with CLAUDE_CODE_GZIP_REQUEST_BODIES=1.

Evidence

(search for "CLAUDE_CODE_GZIP_REQUEST_BODIES", "tengu_gzip_request_bodies", yGd() call at the fetch wrapper, wce(l) host check at line ~161308)

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.199 →