GPT-5 Codex
CodingClosed weightsTextReasoning
GPT Codex family model by OpenAI.
About the GPT Codex family
OpenAI's coding-specialized GPT-5-series models powering the Codex agent — optimized for repository-scale software engineering, debugging and long agentic coding sessions.
All GPT Codex modelsHow this one is configured
This configuration runs in reasoning mode (thinks step-by-step before answering).
Also runs at: high effort
Effort controls how long the model thinks before answering — higher effort usually means better answers on hard problems, at the cost of speed and money. Same model underneath, so they share this page.