upstream_ttfb_ms
A Claude Code settings key, read out of the shipped bundle. It has been in the build since v2.1.287, including the newest one read.
The apps gateway's first-byte timeout setting is now optional, upstreams accept a models list, and Bedrock upstreams can count tokens
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.295.
In the changelogs
2Releases whose published page names upstream_ttfb_ms.
-
v2.1.295
Apps gateway: tunable first-byte timeout, model lists and Bedrock token counting
The apps gateway's first-byte timeout setting is now optional, upstreams accept a models list, and Bedrock upstreams can count tokens
found in this entry's text
-
v2.1.295
Gateway first-byte timeout now covers non-Anthropic upstreams
timeouts.upstream_ttfb_msnow also applies to streaming and token-count requests sent to non-Anthropic upstreamsfound in this entry's text
First cited
1The earliest release whose published evidence quoted upstream_ttfb_ms was v2.1.295, 8 Oct 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
9One 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 settings key does. All settings keys.