Gemini 3 Flash vs GPT-5.3-Codex
Gemini 3 Flash 
GPT-5.3-Codex Verdict
- Gemini 3 Flash (thinking) and GPT-5.3-Codex are level on quality (61.6 vs 62.5).
- Gemini 3 Flash (thinking) is stronger in agents & tools, instruction following, multimodal.
- GPT-5.3-Codex is stronger in composite, knowledge, long context, coding.
- Gemini 3 Flash (thinking) is 4.3× cheaper ($1.13 vs $4.81 per 1M blended).
- Gemini 3 Flash (thinking) streams 1.5× faster (180 vs 121 tokens per second).
| Metric | Gemini 3 Flash (thinking) | GPT-5.3-Codex |
|---|---|---|
| BenchLeader Index | 61.6 | 62.5 |
| Agents & tools score | 67.4 | 62.7 |
| Composite score | 62.3 | 70.1 |
| Instruction following score | 75.4 | 73.2 |
| Knowledge score | 69.0 | 69.3 |
| Long context score | 65.5 | 68.3 |
| Multimodal score | 64.4 | 63.0 |
| Coding score | – | 54.8 |
| Blended price $/M | $1.13 | $4.81 |
| Output speed | 180 tok/s | 121 tok/s |
| Time to first answer | 6.1 s | 58.2 s |
| Context window | 1M | 400k |
| Terminal-Bench | – | 78.4% |
| WeirdML | – | 79.3% |
| APEX-Agents | – | 31.8% |
| Epoch Capabilities Index | – | 156.6 |
| LMArena WebDev | – | 1409 |
| AA Intelligence Index | 26.3 | 32.5 |
| IFBench | 78.0% | 75.4% |
| AA-LCR | 78.0% | 83.3% |
| MMMU-Pro | 79.9% | 78.5% |
| AA-Omniscience | 10.1 | 10.9 |
| Terminal-Bench Hard | 38.6% | 53.0% |
| GPQA Diamond (AA) | 89.8% | 91.5% |
| Humanity's Last Exam (AA) | 36.6% | 42.5% |
| τ²-Bench Telecom (AA) | 80.4% | 86.0% |
| 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.
Gemini 3 Flash vs GPT-5.3-Codex: questions
- Is Gemini 3 Flash better than GPT-5.3-Codex?
- Gemini 3 Flash (thinking) and GPT-5.3-Codex are level on quality (61.6 vs 62.5). 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 Gemini 3 Flash better than GPT-5.3-Codex for agentic tasks?
- Gemini 3 Flash scores higher in agentic tasks (67 vs 63 on the category index, where 50 is average).
- Which is cheaper, Gemini 3 Flash or GPT-5.3-Codex?
- Gemini 3 Flash is cheaper: $1.13 against $4.81 per million tokens, blended at three input tokens per output token.
- Which is faster, Gemini 3 Flash or GPT-5.3-Codex?
- Gemini 3 Flash streams faster: 180 against 121 output tokens per second.
- Which has the larger context window?
- Gemini 3 Flash accepts more context: 1M against 400k tokens.