Claude's token-efficient tools header has no page left to check (2026)

On 11 October 2026 I set out to delete two beta headers from a request builder nobody had touched in a year. One of them, token-efficient-tools-2025-02-19, no longer has a page. The URL that used to define it now returns a 307 to a migration guide index that mentions neither the feature nor beta headers at all.

The entire surviving description of what that header does is one sentence on one of Anthropic's four model migration guides. It says the headers have no effect. That tells you about the effect. It does not tell you whether the name is still accepted, and the same documentation set is unusually careful about that distinction everywhere else.

The builder had an anthropic-beta line with two comma-separated values in it, added by someone who left, pinned by nothing, covered by no test. token-efficient-tools-2025-02-19 and output-128k-2025-02-19.