Model Drop

GPT-5-Codex

September 15, 2025 1 min read

GPT-5-Codex, which OpenAI shipped in Codex on September 15, 2025 (API access followed on September 23), is a version of GPT-5 tuned for agentic coding and code review.

Model: GPT-5-Codex (gpt-5-codex)
Maker: OpenAI
Ship date: September 15, 2025
Pricing: Paid ChatGPT plans (Codex) at launch; API from September 23 at $1.25 / $10 per M tokens
Context: 272K input tokens (400K total with output)
Weights: Closed
Where you can use it:
- Codex CLI, IDE extension, cloud and GitHub
- Responses API from September 23
When to reach for it:
- Big refactors and long agent runs
- Automated pull request reviews
- Skip it outside agentic coding work
How it compares:
- Edges GPT-5 and Claude Opus 4.1 overall
- Well ahead of Grok Code Fast 1
What makes it different:
- Fast on small asks, runs hours on big ones
- Trained specifically to review code
Early reactions: Developers praised its code reviews and persistence on long tasks, but some found it erratic and slower than Claude for quick prompts.
Read more: Introducing upgrades to Codex, Addendum to GPT-5 system card: GPT-5-Codex

The benchmarks

OpenAI ran both models at high reasoning effort (SWE-bench Verified on all 500 tasks) and compared GPT-5-Codex only with GPT-5; the refactoring and code-review evals are internal, and GPT-5-Codex trails GPT-5 on none of the rows OpenAI published.

OpenAI's numbers

SWE-bench Verified (real GitHub fixes): 74.5%. +1.7 over GPT-5 (high) (72.8%).
Code refactoring tasks (large-repo refactors): 51.3%. +17.4 over GPT-5 (high) (33.9%).
Code review high-impact comments (share of comments): 52.4%. +13.0 over GPT-5 (high) (39.4%).
Code review incorrect comments (lower is better): 4.4%. −9.3 under GPT-5 (high) (13.7%).
Code review comments per PR (average count): 0.93. −0.39 under GPT-5 (high) (1.32).

Independent numbers

Artificial Analysis Intelligence Index (current v4.3.2, AA estimate): 24.9. +1.9 over GPT-5 (23.0), +2.1 over Claude Opus 4.1 (22.8), +8.8 over Gemini 2.5 Pro (16.1), +10.8 over Grok Code Fast 1 (14.1).