Claude Sonnet 4.5 vs GPT-5-Codex
Anthropic Claude Sonnet 4.5 | OpenAI GPT-5-Codex | |
|---|---|---|
| Overview | ||
| Company | Anthropic | OpenAI |
| Release date | Sep 29 2025 | Sep 15 2025 |
| Access | Proprietary | Proprietary |
| Benchmarks | ||
Nonsense detection BullshitBench v2Given a confidently-worded but nonsensical prompt, does the AI spot that it makes no sense and push back — instead of playing along and inventing an answer? The score is how often it clearly called out the nonsense. Higher is better. | 79%Best | 39% |
Coding SWE-Bench VerifiedReal coding tasks pulled from open-source projects — the AI has to find and fix actual bugs. A human-checked version of the original SWE-Bench. Higher is better. | 77.2% | — |
Next.js coding Next.js EvalsVercel's open eval of how well AI coding agents build and migrate real Next.js apps — measured as the share of tasks the agent completes successfully. Higher is better. | 50% | — |
Science GPQA DiamondGraduate-level science questions in biology, physics, and chemistry — hard enough that subject-matter PhDs score around 65%. Higher is better. | 83.4% | — |
Multimodal MMMUTests the AI on understanding images and text together across many college subjects. Higher is better. | 68% | — |
| Timeline | ||
| Release gap | GPT-5-Codex shipped 14 days before Claude Sonnet 4.5 | |
Which is better: Claude Sonnet 4.5 or GPT-5-Codex?
Claude Sonnet 4.5 leads GPT-5-Codex on 1 of the 1 benchmark they both report (BullshitBench v2). GPT-5-Codex shipped 14 days before Claude Sonnet 4.5, so benchmark comparisons should account for the intervening progress.
Published specifications for these two models are limited — see each model page for the latest details.
On BullshitBench v2, Claude Sonnet 4.5 leads at 79% vs GPT-5-Codex at 39%.
Frequently asked questions
Claude Sonnet 4.5 was released by Anthropic on Sep 29 2025.
GPT-5-Codex was released by OpenAI on Sep 15 2025.
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