Story · Vercel
Claude Opus 5.5 now available on AI Gateway (Vercel)
blog post · via METR · Story page
Two API changes turn previously valid requests into HTTP 400: thinking is always adaptive, so disabling it or setting a fixed budget is rejected, and forced tool use is retired. Vercel says Anthropic cites Fable 5.1-level performance at roughly 30% faster and 40% cheaper per task than Opus 5.
In plain words
- Vercel now offers software developers access to Claude Opus 5.5, an artificial intelligence system from Anthropic.
- Anthropic reports roughly 30% faster work at roughly 40% lower cost per task than Opus 5.
- The system chooses how much to think, rejecting requests that turn thinking off or set a fixed allowance.
- It also rejects requests that force it to use tools, meaning other software it can ask to perform tasks.
- Developers connecting software to this version must adjust affected requests to avoid failures.
Appeared in
- Dormant prompt injections land on nine production agents where direct orders fail
Sep 23, 2026 · in the sections
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