Answer · Coding
What AI models does Codex use?
Codex runs on 5.6 Sol (OpenAI), GPT-4 (OpenAI), GPT-5.2 (OpenAI), GPT-5.2-Codex (OpenAI), GPT-5.4 (OpenAI), GPT-5.6 (OpenAI), GPT-5.6 Luna (OpenAI), GPT-5.6 Sol (OpenAI), GPT-5.6 Terra (OpenAI), GPT-6 Astra (OpenAI), GPT-Live (OpenAI) and gpt-oss (OpenAI), and routes requests between them.
- Models used
- 12
- Primary model
- 5.6 Sol
- Public API
- Yes
- Last checked
- 2026-09-12
Model claims are labelled by how we know them: 5.6 Sol — disclosed, GPT-4 — inferred, GPT-5.2 — disclosed, GPT-5.2-Codex — disclosed, GPT-5.4 — inferred, GPT-5.6 — disclosed, GPT-5.6 Luna — disclosed, GPT-5.6 Sol — disclosed, GPT-5.6 Terra — disclosed, GPT-6 Astra — disclosed, GPT-Live — disclosed and gpt-oss — inferred. "Disclosed" means the vendor says so in public; "inferred" means it was derived from documentation, headers or release notes.
Context window: 400K tokens.
Other stack signals: Rust CLI, Container sandbox and MCP.
Cite this answer
Tomorrow. “What AI models does Codex use?” Tomorrow AI & Emerging Tech Index, AlienSquad, updated 2026-09-12. https://tomorrow.aliensquad.ai/q/what-models-does-codex-use
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