Act on this, mostly signal

Claude API version 2026-10-21 removes temperature, top_p and top_k

What to do

Check code that sets temperature, top_p or top_k before upgrading, since the new version drops them from the Messages API.

Why

SDK and ant CLI majors now default to this version, and 2023-06-01 stays supported.

Read the source at phemex.com

What the research found

Claude API version 2026-10-21, the first dated version since 2023, removes temperature, top_p and top_k from the Messages API; the 2023-06-01 version stays supported and SDK majors default to the new version.

Claims and how well the evidence supports them

Claude API version 2026-10-21 removes temperature, top_p and top_k from the Messages API 99%
The legacy 2023-06-01 API version remains supported 99%
Passing documents in an assistant turn or citations in a user turn now returns a 400 error 99%
Anthropic SDK new major versions default to API version 2026-10-21 98%

Evidence

phemex.com https://phemex.com/news/article/anthropic-ships-first-claude-api-version-since-2023-drops-temperature-and-topp-parameters-100292

Actionability rated high.