OpenAI: gpt-5-codex API
A specialized coding version of GPT-5 released in September 2025. Built on GPT-5's native reasoning, it is fine-tuned for logical understanding of massive codebases, cross-file refactoring, and complex bug fixing. Featuring "Repo-aware" intelligence, it achieves a 74.5% success rate on SWE-bench (Verified) and strictly adheres to complex developer instructions in .cursorrules or the Codex CLI.
- Context window: 400,000 tokens
- Max output: 128,000 tokens
- Input: text, image
- Output: text
- Reasoning: Supported
- Tool calling: Supported
- File input: Supported
- Released: 2025-09-15
- Knowledge cutoff: 2024-09-30
Frequently Asked Questions
What is the context window of gpt-5-codex?
gpt-5-codex supports a context window of up to 400,000 tokens.
Does gpt-5-codex support function calling?
Yes. gpt-5-codex supports tool / function calling.
Does gpt-5-codex support reasoning?
Yes. gpt-5-codex is a reasoning-capable model.
What is the knowledge cutoff of gpt-5-codex?
The knowledge cutoff of gpt-5-codex is 2024-09-30.