GPT-5.3-Codex vs GPT-5.5 Instant
GPT-5.3-Codex Verdict
- GPT-5.3-Codex leads on quality: 62.5 vs 60.5.
- GPT-5.3-Codex is stronger in composite, instruction following, long context, multimodal.
- GPT-5.5 Instant is stronger in agents & tools, coding, knowledge, human preference, maths, reasoning.
- GPT-5.3-Codex is 2.3× cheaper ($4.81 vs $11.25 per 1M blended).
| Metric | GPT-5.3-Codex | GPT-5.5 Instant |
|---|---|---|
| BenchLeader Index | 62.5 | 60.5 |
| Agents & tools score | 62.7 | 70.7 |
| Coding score | 54.8 | 61.1 |
| Composite score | 70.1 | 62.9 |
| Instruction following score | 73.2 | 69.8 |
| Knowledge score | 69.3 | 69.4 |
| Long context score | 68.3 | 61.4 |
| Multimodal score | 63.0 | 59.7 |
| Human preference score | – | 67.5 |
| Maths score | – | 42.5 |
| Reasoning score | – | 62.6 |
| Blended price $/M | $4.81 | $11.25 |
| Output speed | 121 tok/s | 129 tok/s |
| Time to first answer | 58.2 s | 16.8 s |
| Context window | 400k | 400k |
| GPQA Diamond | – | 82.5% |
| FrontierMath Tiers 1–3 | – | 26.3% |
| FrontierMath Tier 4 | – | 2.4% |
| OTIS Mock AIME | – | 68.1% |
| Terminal-Bench | 78.4% | – |
| SciCode | – | 48.6% |
| WeirdML | 79.3% | – |
| APEX-Agents | 31.8% | – |
| Epoch Capabilities Index | 156.6 | 142.5 |
| LMArena Text | – | 1474 |
| LMArena Hard Prompts | – | 1491 |
| LMArena Coding | – | 1514 |
| LMArena WebDev | 1409 | – |
| LMArena Vision | – | 1251 |
| AA Intelligence Index | 32.5 | 26.8 |
| IFBench | 75.4% | 71.5% |
| AA-LCR | 83.3% | 70.0% |
| MMMU-Pro | 78.5% | – |
| AA-Omniscience | 10.9 | 11.2 |
| Terminal-Bench Hard | 53.0% | 42.4% |
| GPQA Diamond (AA) | 91.5% | 84.7% |
| Humanity's Last Exam (AA) | 42.5% | 21.6% |
| SciCode (AA) | – | 52.5% |
| τ²-Bench Telecom (AA) | 86.0% | 49.4% |
| HiL-Bench | 4.3% | – |
Data as of 2026-09-10. Best configuration of each model; every score links to its source on the model pages.
GPT-5.3-Codex vs GPT-5.5 Instant: questions
- Is GPT-5.3-Codex better than GPT-5.5 Instant?
- GPT-5.3-Codex leads on quality: 62.5 vs 60.5. 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 GPT-5.3-Codex better than GPT-5.5 Instant for coding?
- GPT-5.5 Instant scores higher in coding (61 vs 55 on the category index, where 50 is average).
- Is GPT-5.3-Codex better than GPT-5.5 Instant for agentic tasks?
- GPT-5.5 Instant scores higher in agentic tasks (71 vs 63 on the category index, where 50 is average).
- Which is cheaper, GPT-5.3-Codex or GPT-5.5 Instant?
- GPT-5.3-Codex is cheaper: $4.81 against $11.25 per million tokens, blended at three input tokens per output token.
- Which is faster, GPT-5.3-Codex or GPT-5.5 Instant?
- GPT-5.5 Instant streams faster: 129 against 121 output tokens per second.
- Which has the larger context window?
- Both accept 400k tokens of context.