GPT-5.3-Codex vs o3
GPT-5.3-Codex Verdict
- GPT-5.3-Codex and o3 are level on quality (62.5 vs 61.6).
- GPT-5.3-Codex is stronger in composite, instruction following, knowledge, long context, multimodal.
- o3 is stronger in agents & tools, coding, human preference, maths, reasoning.
- o3 is 1.4× cheaper ($3.50 vs $4.81 per 1M blended).
| Metric | GPT-5.3-Codex | o3 |
|---|---|---|
| BenchLeader Index | 62.5 | 61.6 |
| Agents & tools score | 62.7 | 70.3 |
| Coding score | 54.7 | 62.0 |
| Composite score | 70.1 | 54.5 |
| Instruction following score | 73.2 | 65.0 |
| Knowledge score | 69.4 | 58.0 |
| Long context score | 68.3 | 63.8 |
| Multimodal score | 63.0 | 57.9 |
| Human preference score | – | 62.3 |
| Maths score | – | 78.6 |
| Reasoning score | – | 61.5 |
| Blended price $/M | $4.81 | $3.50 |
| Output speed | 121 tok/s | 107 tok/s |
| Time to first answer | 51.6 s | 6.3 s |
| Context window | 400k | 200k |
| Terminal-Bench | 78.4% | – |
| WeirdML | 79.3% | – |
| APEX-Agents | 31.8% | – |
| Epoch Capabilities Index | 156.6 | 146.9 |
| LMArena Text | – | 1432 |
| LMArena Hard Prompts | – | 1441 |
| LMArena Coding | – | 1460 |
| LMArena WebDev | 1409 | – |
| LMArena Vision | – | 1214 |
| AA Intelligence Index | 32.5 | 20.2 |
| IFBench | 75.4% | 71.4% |
| AA-LCR | 83.3% | 74.7% |
| MMMU-Pro | 78.5% | 70.1% |
| AA-Omniscience | 10.9 | -15.6 |
| Terminal-Bench Hard | 53.0% | 37.1% |
| GPQA Diamond (AA) | 91.5% | 82.7% |
| Humanity's Last Exam (AA) | 42.5% | 20.1% |
| τ²-Bench Telecom (AA) | 86.0% | 80.7% |
| PRBench Finance | – | 47.7% |
| PRBench Legal | – | 48.6% |
| HiL-Bench | 4.3% | – |
| MMMU (validation) | – | 82.9% |
| MMMU-Pro (official) | – | 76.4% |
| Kagi LLM Benchmark | – | 67.6% |
| IFEval (HELM) | – | 86.9% |
| Omni-MATH (HELM) | – | 71.4% |
| WildBench (HELM) | – | 86.1% |
| MMLU-Pro (HELM) | – | 85.9% |
| GPQA Diamond (HELM) | – | 75.3% |
| HELM Capabilities mean | – | 81.1% |
| Aider Polyglot | – | 81.3% |
| SWE-bench Verified (bash only) | – | 58.4% |
| SWE-bench Verified (any scaffold) | – | 58.4% |
| BFCL Overall | – | 63.0% |
Data as of 2026-09-12. Best configuration of each model; every score links to its source on the model pages.
GPT-5.3-Codex vs o3: questions
- Is GPT-5.3-Codex better than o3?
- GPT-5.3-Codex and o3 are level on quality (62.5 vs 61.6). The BenchLeader Index combines every independent quality benchmark; GPT-5.3-Codex is ahead overall as of 2026-09-12, but check the category scores for your use.
- Is GPT-5.3-Codex better than o3 for coding?
- o3 scores higher in coding (62 vs 55 on the category index, where 50 is average).
- Is GPT-5.3-Codex better than o3 for agentic tasks?
- o3 scores higher in agentic tasks (70 vs 63 on the category index, where 50 is average).
- Which is cheaper, GPT-5.3-Codex or o3?
- o3 is cheaper: $3.50 against $4.81 per million tokens, blended at three input tokens per output token.
- Which is faster, GPT-5.3-Codex or o3?
- GPT-5.3-Codex streams faster: 121 against 107 output tokens per second.
- Which has the larger context window?
- GPT-5.3-Codex accepts more context: 400k against 200k tokens.