Claude Sonnet 4.5 retires from the Claude API on November 30
11/11/2026 — 11/11, 13:18·1 sources (all)·1 reports (all)
Key takeaways
- Anthropic will retire claude-sonnet-4-5-20250929 from the Claude API on November 30;
- requests will then error out rather than fall back to a similar model, and Claude Opus 4.8's fast mode is removed the same day. Since API ve…
Background & analysis
Anthropic is retiring claude-sonnet-4-5-20250929 from the Claude API on November 30, 2026, according to a DEV Community post published on November 11, 2026. After that date, requests sent to this model identifier do not degrade and do not fall back to a close alternative. They fail outright with an error. The same day, fast mode for Claude Opus 4.8 is removed, and requests routed that way also end in an error.
The post sets out two dates that frame the migration. On 2026-09-30, claude-sonnet-4-5-20250929 was marked Deprecated, with a notice period of 61 days. Then API version 2026-10-21 is where temperature, top_p, and top_k begin returning 400, so renaming the model is not enough on its own: teams need to find the old identifiers still present in their code and configuration, then rerun their own use cases against whatever they have moved to.
One fragment adds that as of November 9 the retirement was 21 days away, and it refers to release notes dated 2026-10-30 that mention fast m. The sentence is cut off in the source, so the detail is not verifiable. The source material consists of a single report, with no Anthropic announcement or follow-up coverage, and it does not name a successor model. No further developments have been recorded beyond the November 30, 2026 date.
AI-generated from 1 reports · updated 2 days ago
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Reports on this story headlines open the original
Anthropic will retire claude-sonnet-4-5-20250929 from the Claude API on November 30, after which requests fail with an error rather than falling back to a nearby model; fast mode for Claude Opus 4.8 is removed the same day. The post notes that since API version 2026-10-21, temperature, top_p and top_k return a 400, so swapping the model string alone may not be enough.
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