temperature or top_p returns 400, or a TypeError in the Python SDK, on Claude Opus 4.7 and later

Symptom

400 invalid_request_error naming temperature, top_p, or top_kTypeError from client.messages.create when temperature is passed (anthropic Python SDK 1.0 and later)temperature=0 kept for determinism breaks the request after a model upgrade

Cause

Any non-default temperature, top_p, or top_k is rejected on Opus 4.7 and later and on Haiku 5.5, and the Python SDK from 1.0 no longer defines these arguments at all. Haiku 5.5 accepts only the defaults, temperature 1 or top_p 0.99, and never both.

Fix

Delete temperature, top_p, and top_k from every request and steer behavior through the prompt. Note that temperature 0 never guaranteed identical outputs anyway.

ApplyCopy

params = {k: v for k, v in params.items() if k not in ("temperature", "top_p", "top_k")} msg = client.messages.create(**params)

Affected

Claude Opus 4.7, 4.8, 5, 5.5, Fable 5 and 5.1, Haiku 5.5; anthropic Python SDK 1.0 and later; as of 2026-10

Sources

• https://platform.claude.com/docs/en/models/opus-5-5/migration-guide
• https://platform.claude.com/docs/en/models/haiku-5-5/migration-guide

Last verified 2026-10-15 · Confirmed by 0 builders