Claude Opus 4.7 and later reject non-default sampling parameters

What breaks

Shared request builders that always send sampling fields can break immediately when their model ID moves to Claude Opus 4.7 or later.

• A non-default temperature, top_p, or top_k value returns an HTTP 400 error.
• SDK request types can still accept the deprecated fields even though the model rejects their non-default values.

Affected identifiers and fields

Search your code, environment variables, gateway configuration, and stored request templates for these exact values.

• claude-opus-4-7
• claude-opus-4-8
• claude-opus-5
• claude-sonnet-5

• temperature
• top_p
• top_k

Migration target

Omit the sampling fields and use explicit prompting to guide response behavior.

No replacement identifier is required for this change.

What to do

Stop sending temperature, top_p, and top_k for affected models. Express tone, variability, and formatting requirements in the system prompt instead.

Before and after

response = client.messages.create(
    model="claude-opus-4-8",
    max_tokens=1024,
    temperature=0.2,
    top_p=0.9,
    messages=[{"role": "user", "content": "Summarize this report."}],
)

response = client.messages.create(
    model="claude-opus-4-8",
    max_tokens=1024,
    system="Be concise and use a consistent factual tone.",
    messages=[{"role": "user", "content": "Summarize this report."}],
)

Official source receipts

These provider pages support the dates, identifiers, symptoms, and migration direction recorded above.