GPT-5.3-Codex

GPT-5.3-Codex is OpenAI's coding-specialized model from the GPT-5.3 generation, built for software development tasks with a 400k token context window.

Strengths

Handles code generation, analysis, and completion across large codebases and multi-file contexts within its extended token window.

Best for

Development workflows that require understanding and working with substantial amounts of source code and technical documentation.

Limitations

Superseded by newer models in the GPT-5.4 lineup released in March 2026, which offer improved reasoning and inference capabilities across both general and specialized tasks.