Claude "temperature is deprecated for this model" (400)

Your request worked on an older Claude model. You change the model name and get a 400 about a parameter you’ve been sending for months. This is going to hit a lot of people soon: Claude Sonnet 4.5 retires on November 30, 2026, and Anthropic’s recommended replacement, claude-sonnet-5-5, is one of the models that rejects it.

I sent the same one-word request to six Claude models with each sampling parameter set, in Node and in Python. The rule turned out to be sharper than “temperature is deprecated”.

Which values fail, on which models

Two things stand out:

• temperature: 0 is rejected. That’s the value people set on purpose, for repeatable output, so it’s exactly the code that breaks. Only 1 gets through, because it’s the default.
• The older models have their own trap. Opus 4.6 and Haiku 4.5 accept each parameter on its own, but not temperature and top_p together. Code that sets both already fails there.

The error is an invalid_request_error, in Node a BadRequestError with status 400. It names the first parameter it rejects, so after you remove temperature you may get the same message for top_p.

The fix

const msg = await client.messages.create({
  model: 'claude-sonnet-5-5',
  max_tokens: 1024,
  // temperature: 0,   <- delete
  // top_p: 0.9,       <- delete
  messages: [{ role: 'user', content: 'Hello' }],
});

const legacy = ['claude-opus-4-6', 'claude-haiku-4-5-20251001'];
const sampling = legacy.includes(model) ? { temperature: 0 } : {};
await client.messages.create({ model, max_tokens: 1024, messages, ...sampling });

Python: a TypeError before the request is even sent

The Python SDK went further. Since anthropic 1.0.0 (I checked 1.0.0 through 1.17.0 and 2.1.0), temperature, top_p and top_k are gone from messages.create() entirely, so the error comes from Python itself, for every model, including the ones that still accept it:

TypeError: Messages.create() got an unexpected keyword argument 'temperature'

So upgrading the Python SDK breaks code that ran fine against Haiku 4.5 or Opus 4.6, before you’ve changed any model name.

msg = client.messages.create(
    model="claude-haiku-4-5-20251001",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello"}],
    extra_body={"temperature": 0.2},
)

Since October 21: the API rejects it on every model

On October 21, 2026, Anthropic released API version 2026-10-21, and the new SDKs (anthropic 2.0.0 for Python, @anthropic-ai/sdk 1.0.0 for TypeScript) send it by default. Anthropic’s migration guide says a 2026-10-21 request with temperature, top_p or top_k returns a 400 on any model, even at the default value. So the extra_body bridge above stops working once you upgrade.

I tested that on November 7 with @anthropic-ai/sdk 1.6.0, which sent anthropic-version: 2026-10-21. temperature: 0 and temperature: 1 both failed on Haiku 4.5 as well as Haiku 5.5, with a different message from the one at the top of this page (status and message as the SDK reported them):

400 temperature: Extra inputs are not permitted

On Python 2.1.0, one request can still be kept on the old API version, where older models take the parameter. That line and the other SDK 2.0 errors, with tests, are in unexpected keyword argument temperature, betas.

Sonnet 4.5 may already be gone for you

Anthropic lists claude-sonnet-4-5-20250929 as deprecated, retiring November 30. With my API key it was already unavailable on October 11. Every call returned:

NotFoundError: 404 {"type":"error","error":{"type":"not_found_error","message":"model: claude-sonnet-4-5-20250929"}}

The Node SDK also printed its own warning before each call: Please migrate to a newer model. Visit https://docs.anthropic.com/en/docs/resources/model-deprecations for more information. If you see that line in your logs, the model in your code is on the retirement list.

My key belongs to a newer organization, which may never have had Sonnet 4.5. Anthropic’s page says requests fail after the retirement date, so an account that has been using it should keep it until then. Either way, the replacement is Sonnet 5.5, and moving to it is when the temperature error appears.

How this was tested

Six models (claude-sonnet-4-5-20250929, claude-sonnet-5-5, claude-haiku-4-5-20251001, claude-haiku-5-5, claude-opus-4-6, claude-opus-4-7), each called with no sampling parameters, temperature 0, 0.2 and 1, top_p 0.9, top_k 40, and temperature with top_p. Node used @anthropic-ai/sdk 0.133.0 on Node 24, Python used anthropic 1.13.0 on Python 3.13, both on October 11, 2026. Every request asked for a single output token. The retirement date and replacement are from Anthropic’s model deprecations page.