concepts/subagents.md Codex Docs, 2026-05-12 01:59 UTC → 2026-05-13 00:57 UTC

66If you don't pin a model or `model_reasoning_effort`, Codex can choose a setup66If you don't pin a model or `model_reasoning_effort`, Codex can choose a setup

67that balances intelligence, speed, and price for the task. It may favor67that balances intelligence, speed, and price for the task. It may favor

68`gpt-5.4-mini` for fast scans or a higher-effort `gpt-5.5` configuration for68`gpt-5.4-mini` for fast scans or a higher-effort `gpt-5.5` configuration for

69more demanding reasoning when that model is available. When you want finer69more demanding reasoning. When you want finer control, steer that choice in

70control, steer that choice in your prompt or set `model` and70your prompt or set `model` and

71`model_reasoning_effort` directly in the agent file.71`model_reasoning_effort` directly in the agent file.

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73For most tasks in Codex, start with `gpt-5.5` when it is available. Continue73For most tasks in Codex, start with `gpt-5.5`. Use `gpt-5.4-mini` when you

74 using `gpt-5.4` during the rollout if `gpt-5.5` is not yet available. Use74 want a faster, lower-cost option for lighter subagent work. If you have

75 `gpt-5.4-mini` when you want a faster, lower-cost option for lighter subagent75 ChatGPT Pro and want near-instant text-only iteration, `gpt-5.3-codex-spark`

76 work. If you have ChatGPT Pro and want near-instant text-only iteration,76 remains available in research preview.

77 `gpt-5.3-codex-spark` remains available in research preview.

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79### Model choice78### Model choice

80 79 

81- **`gpt-5.5`**: Start here for demanding agents when it is available. It is strongest for ambiguous, multi-step work that needs planning, tool use, validation, and follow-through across a larger context.80- **`gpt-5.5`**: Start here for demanding agents. It is strongest for ambiguous, multi-step work that needs planning, tool use, validation, and follow-through across a larger context.

82- **`gpt-5.4`**: Use this when `gpt-5.5` is not yet available or when a workflow is pinned to GPT-5.4. It combines strong coding, reasoning, tool use, and broader workflows.81- **`gpt-5.4`**: Use this when a workflow is pinned to GPT-5.4. It combines strong coding, reasoning, tool use, and broader workflows.

83- **`gpt-5.4-mini`**: Use for agents that favor speed and efficiency over depth, such as exploration, read-heavy scans, large-file review, or processing supporting documents. It works well for parallel workers that return distilled results to the main agent.82- **`gpt-5.4-mini`**: Use for agents that favor speed and efficiency over depth, such as exploration, read-heavy scans, large-file review, or processing supporting documents. It works well for parallel workers that return distilled results to the main agent.

84- **`gpt-5.3-codex-spark`**: If you have ChatGPT Pro, use this research preview model for near-instant, text-only iteration when latency matters more than broader capability.83- **`gpt-5.3-codex-spark`**: If you have ChatGPT Pro, use this research preview model for near-instant, text-only iteration when latency matters more than broader capability.

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