Claude Opus 4.5 vs GPT-5.3-Codex
Claude Opus 4.5 
GPT-5.3-Codex Verdict
- GPT-5.3-Codex leads on quality: 62.5 vs 60.7.
- Claude Opus 4.5 (thinking) is stronger in agents & tools, coding, maths, reasoning.
- GPT-5.3-Codex is stronger in composite, instruction following, knowledge, long context, multimodal.
- GPT-5.3-Codex is 2.1× cheaper ($4.81 vs $10.00 per 1M blended).
- GPT-5.3-Codex streams 2.7× faster (121 vs 45 tokens per second).
| Metric | Claude Opus 4.5 (thinking) | GPT-5.3-Codex |
|---|---|---|
| BenchLeader Index | 60.7 | 62.5 |
| Agents & tools score | 74.6 | 62.7 |
| Coding score | 56.4 | 54.8 |
| Composite score | 65.8 | 70.1 |
| Instruction following score | 54.8 | 73.2 |
| Knowledge score | 61.0 | 69.3 |
| Long context score | 65.2 | 68.3 |
| Maths score | 64.0 | – |
| Multimodal score | 58.0 | 63.0 |
| Reasoning score | 58.6 | – |
| Blended price $/M | $10.00 | $4.81 |
| Output speed | 45 tok/s | 121 tok/s |
| Time to first answer | 17.3 s | 58.2 s |
| Context window | 200k | 400k |
| Terminal-Bench | – | 78.4% |
| WeirdML | – | 79.3% |
| APEX-Agents | – | 31.8% |
| Epoch Capabilities Index | – | 156.6 |
| LMArena WebDev | – | 1409 |
| AA Intelligence Index | 29.1 | 32.5 |
| IFBench | 58.0% | 75.4% |
| AA-LCR | 77.3% | 83.3% |
| MMMU-Pro | 74.0% | 78.5% |
| AA-Omniscience | 14 | 10.9 |
| Terminal-Bench Hard | 47.0% | 53.0% |
| GPQA Diamond (AA) | 86.6% | 91.5% |
| Humanity's Last Exam (AA) | 30.1% | 42.5% |
| τ²-Bench Telecom (AA) | 89.5% | 86.0% |
| AIME (Vals) | 95.4% | – |
| LiveCodeBench | 83.7% | – |
| MMLU-Pro | 87.3% | – |
| IOI | 20.3% | – |
| LegalBench | 84.6% | – |
| CorpFin | 65.1% | – |
| TaxEval | 74.9% | – |
| MedQA | 95.9% | – |
| MGSM | 95.2% | – |
| SWE-bench (Vals) | 76.4% | – |
| GPQA Diamond (Vals) | 85.9% | – |
| MultiChallenge | 59.0% | – |
| PRBench Finance | 46.2% | – |
| PRBench Legal | 44.2% | – |
| VISTA | 46.4% | – |
| MultiNRC | 48.6% | – |
| HiL-Bench | – | 4.3% |
| TutorBench | 51.2% | – |
| Kagi LLM Benchmark | 80.2% | – |
| ARC-AGI-1 | 80.0% | – |
| ARC-AGI-2 | 37.6% | – |
Data as of 2026-09-10. Best configuration of each model; every score links to its source on the model pages.
Claude Opus 4.5 vs GPT-5.3-Codex: questions
- Is Claude Opus 4.5 better than GPT-5.3-Codex?
- GPT-5.3-Codex leads on quality: 62.5 vs 60.7. The BenchLeader Index combines every independent quality benchmark; GPT-5.3-Codex is ahead overall as of 2026-09-10, but check the category scores for your use.
- Is Claude Opus 4.5 better than GPT-5.3-Codex for coding?
- Claude Opus 4.5 scores higher in coding (56 vs 55 on the category index, where 50 is average).
- Is Claude Opus 4.5 better than GPT-5.3-Codex for agentic tasks?
- Claude Opus 4.5 scores higher in agentic tasks (75 vs 63 on the category index, where 50 is average).
- Which is cheaper, Claude Opus 4.5 or GPT-5.3-Codex?
- GPT-5.3-Codex is cheaper: $4.81 against $10.00 per million tokens, blended at three input tokens per output token.
- Which is faster, Claude Opus 4.5 or GPT-5.3-Codex?
- GPT-5.3-Codex streams faster: 121 against 45 output tokens per second.
- Which has the larger context window?
- GPT-5.3-Codex accepts more context: 400k against 200k tokens.