reasoning

Options for reasoning models.

Note that some options, like reasoning summaries, are only available when using the responses API. If these options are set, the responses API will be used to fulfill the request.

These options will be ignored when not using a reasoning model.

Changing this value part-way through a conversation changes a request-level parameter, which invalidates the cached prompt prefix. Models that support it (currently GPT-6) can instead carry the new effort in a configuration_update content block attached to the message that should start using it:

new HumanMessage({
  content: [
    { type: "configuration_update", reasoning: { effort: "high" } },
    { type: "text", text: "Analyze the failure modes." },
  ],
});

The new effort applies from that message onward, until another update overrides it.

Two configuration_update blocks cannot be adjacent in the conversation history, and they cannot be combined with automatic truncation (truncation: "auto") — OpenAI rejects both with an HTTP 400.