Documentation 2026-07-10 23:02 UTC to 2026-07-11 07:01 UTC

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3**Reasoning models** like [GPT-5.5](https://developers.openai.com/api/docs/models/gpt-5.5) use internal reasoning tokens before producing a response. This helps the model plan, use tools effectively, inspect alternatives, recover from ambiguity, and solve harder multi-step tasks. Reasoning models work especially well for complex problem solving, coding, scientific reasoning, and multi-step agentic workflows. They're also the best models for [Codex CLI](https://github.com/openai/codex), our lightweight coding agent.3**Reasoning models** like [GPT-5.5](https://developers.openai.com/api/docs/models/gpt-5.5) use internal reasoning tokens before producing a response. This helps the model plan, use tools effectively, inspect alternatives, recover from ambiguity, and solve harder multi-step tasks. Reasoning models work especially well for complex problem solving, coding, scientific reasoning, and multi-step agentic workflows. They're also the best models for [Codex CLI](https://github.com/openai/codex), our lightweight coding agent.

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5Start with `gpt-5.6` for most reasoning workloads. If you need the highest-intelligence API option for more challenging problems that can tolerate more latency, use [`gpt-5.5-pro`](https://developers.openai.com/api/docs/models/gpt-5.5-pro). For lower cost, consider `gpt-5.4` and for lower cost and latency, consider `gpt-5.4-mini`.5Start with `gpt-5.6` for most reasoning workloads. If you need the highest-intelligence API option for more challenging problems that can tolerate more latency, use <a href="/api/docs/models/gpt-5.6-sol"><code>gpt-5.6-sol</code></a> in the Responses API with `reasoning.mode` set to `pro`. For lower cost, consider `gpt-5.4` and for lower cost and latency, consider `gpt-5.4-mini`.

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7**Reasoning models work better with the [Responses7**Reasoning models work better with the [Responses

8 API](https://developers.openai.com/api/docs/guides/migrate-to-responses)**. While the Chat Completions API8 API](https://developers.openai.com/api/docs/guides/migrate-to-responses)**. While the Chat Completions API