Reasoning mode

GPT-5.6 models support standard and pro reasoning modes in the Responses API. standard is the default. Set reasoning.mode to pro for difficult tasks that need more model work and can tolerate higher latency and token usage.

Reasoning mode and reasoning effort are independent. Mode selects standard or pro execution, while reasoning.effort controls how much reasoning the model applies within that mode. If you omit reasoning.effort, GPT-5.6 defaults to medium in both modes.

Using pro reasoning mode

curl https://api.openai.com/v1/responses \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $OPENAI_API_KEY" \
  -d '{
    "model": "gpt-5.6",
    "reasoning": {
      "mode": "pro",
      "effort": "medium"
    },
    "input": "Review this database migration plan and identify potential failure modes."
  }'

Pro mode aggregates the model work performed to produce the final answer and bills those tokens at the selected model's standard token rates. Pro mode performs more model work than standard mode, increasing token usage and cost. Existing Pro model IDs keep their current behavior and pricing.