GPT-5.1-Codex-Max is the agentic coding model OpenAI shipped in the Codex line in late 2025. In this corpus it appears once, leading PostTrainBench at the recursive task of post-training other models, three days after the Codex product was reported supervising its own training runs; its successors GPT-5.2-Codex and GPT-5.3-Codex carry the line forward.
AISystem
GPT-5.1-Codex-Max
The GPT-5.1-era member of OpenAI's Codex coding-agent line, recorded here as the first leader of PostTrainBench.
Sources
Attribution and reporting linked by this record; links do not imply independent verification.
- Welcome to December 18, 2025 (theinnermostloop.substack.com)
Development timeline
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