Hung requests are aborted when headers never arrive, and you can tune the window.
named in this entry, found in this entry's text
First cited
4
The earliest release whose published evidence quoted CLAUDE_STREAM_FIRST_BYTE_TIMEOUT_MS was v2.1.261, 4 Sep 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.
ReleaseDateThe span that was quoted
v2.1.2614 Sep 2026A proxy or gateway that buffers streaming responses can cause this · set CLAUDE_STREAM_FIRST_BYTE_TIMEOUT_MS to change the first wait
v2.1.2614 Sep 2026Present only when the API sent no response headers within the first-byte window (CLAUDE_STREAM_FIRST_BYTE_TIMEOUT_MS): waited_ms is how long the failed attempt waited for headers, retry_wait_ms how long the retry will wait for them.
v2.1.2614 Sep 2026raise API_TIMEOUT_MS or CLAUDE_STREAM_FIRST_BYTE_TIMEOUT_MS to wait longer
Presence across releases
1
BuildsHow manyDatesReading
v2.1.242 – v2.1.30856 builds24 Aug 2026 → 22 Oct 2026 ◆in the build
Build by build
56
One 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 environment variable does. All environment variables.
