Anthropic ships Claude API version 2026-10-21, rejecting several request patterns with 400
10/22/2026 — 10/22, 16:19·1 sources (all)·1 reports (all)
Key takeaways
- Anthropic released API version 2026-10-21, its first new version since 2023-06-01. Requests that pass temperature, top_p or top_k, place doc…
Background & analysis
On October 21, 2026, Anthropic released Claude API version 2026-10-21, the first new API version since 2023-06-01. DEV Community reported the release the following day, on October 22.
Under the new version, several kinds of requests now return 400. These include requests that send temperature, top_p or top_k, requests that place a document in an assistant message, and requests that put citations in a user message.
Alongside the API version, Anthropic shipped major releases of eight official SDKs and the CLI. These new majors default to 2026-10-21, switch to the Apache 2.0 license, and pass the API key as Authorization: Bearer. Requests that remain on 2023-06-01 continue to work.
The available reporting stops at the version release and the SDK updates. It does not explain why the changes were made or what comes next.
AI-generated from 1 reports · updated 4 hours ago
Latest turnAnthropic released API version 2026-10-21 on October 21, its first new version since 2023-06-01, according to a DEV Community write-up. Requests sending temperature, top_p or top_k on the new version return 400, as do documents in assistant messages and citations in user messages. Eight official SDKs and the CLI shipped new majors that default to the new version and move to Apache 2.0; older pinned requests keep working.
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Anthropic released API version 2026-10-21 on October 21, its first new version since 2023-06-01, according to a DEV Community write-up. Requests sending temperature, top_p or top_k on the new version return 400, as do documents in assistant messages and citations in user messages. Eight official SDKs and the CLI shipped new majors that default to the new version and move to Apache 2.0; older pinned requests keep working.
DEV Community · AIAI score 63
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