Gemini 3.5 Flash vs GPT-5.5 Instant
Gemini 3.5 Flash 
GPT-5.5 Instant Verdict
- Gemini 3.5 Flash (medium) leads on quality: 64.1 vs 60.5.
- Gemini 3.5 Flash (medium) is stronger in composite, human preference, instruction following, knowledge, long context, multimodal, reasoning.
- GPT-5.5 Instant is stronger in agents & tools, coding, maths.
- Gemini 3.5 Flash (medium) is 3.3× cheaper ($3.38 vs $11.25 per 1M blended).
- Gemini 3.5 Flash (medium) streams 1.7× faster (217 vs 129 tokens per second).
| Metric | Gemini 3.5 Flash (medium) | GPT-5.5 Instant |
|---|---|---|
| BenchLeader Index | 64.1 | 60.5 |
| Agents & tools score | 68.0 | 70.7 |
| Coding score | 58.9 | 61.1 |
| Composite score | 71.5 | 62.9 |
| Human preference score | 67.8 | 67.5 |
| Instruction following score | 72.5 | 69.8 |
| Knowledge score | 74.0 | 69.4 |
| Long context score | 63.6 | 61.4 |
| Multimodal score | 67.6 | 59.7 |
| Reasoning score | 67.1 | 62.6 |
| Maths score | – | 42.5 |
| Blended price $/M | $3.38 | $11.25 |
| Output speed | 217 tok/s | 129 tok/s |
| Time to first answer | 15.5 s | 16.8 s |
| Context window | 1M | 400k |
| GPQA Diamond | – | 82.5% |
| FrontierMath Tiers 1–3 | – | 26.3% |
| FrontierMath Tier 4 | – | 2.4% |
| OTIS Mock AIME | – | 68.1% |
| SciCode | – | 48.6% |
| Epoch Capabilities Index | – | 142.5 |
| LMArena Text | 1476 | 1474 |
| LMArena Hard Prompts | 1493 | 1491 |
| LMArena Coding | 1503 | 1514 |
| LMArena WebDev | 1491 | – |
| LMArena Vision | 1306 | 1251 |
| AA Intelligence Index | 33.6 | 26.8 |
| IFBench | 74.6% | 71.5% |
| AA-LCR | 74.3% | 70.0% |
| MMMU-Pro | 83.9% | – |
| AA-Omniscience | 20.8 | 11.2 |
| Terminal-Bench Hard | 39.4% | 42.4% |
| GPQA Diamond (AA) | 92.1% | 84.7% |
| Humanity's Last Exam (AA) | 41.3% | 21.6% |
| SciCode (AA) | – | 52.5% |
| τ²-Bench Telecom (AA) | 95.6% | 49.4% |
Data as of 2026-09-10. Best configuration of each model; every score links to its source on the model pages.
Gemini 3.5 Flash vs GPT-5.5 Instant: questions
- Is Gemini 3.5 Flash better than GPT-5.5 Instant?
- Gemini 3.5 Flash (medium) leads on quality: 64.1 vs 60.5. The BenchLeader Index combines every independent quality benchmark; Gemini 3.5 Flash (medium) is ahead overall as of 2026-09-10, but check the category scores for your use.
- Is Gemini 3.5 Flash better than GPT-5.5 Instant for coding?
- GPT-5.5 Instant scores higher in coding (61 vs 59 on the category index, where 50 is average).
- Is Gemini 3.5 Flash better than GPT-5.5 Instant for agentic tasks?
- GPT-5.5 Instant scores higher in agentic tasks (71 vs 68 on the category index, where 50 is average).
- Which is cheaper, Gemini 3.5 Flash or GPT-5.5 Instant?
- Gemini 3.5 Flash is cheaper: $3.38 against $11.25 per million tokens, blended at three input tokens per output token.
- Which is faster, Gemini 3.5 Flash or GPT-5.5 Instant?
- Gemini 3.5 Flash streams faster: 217 against 129 output tokens per second.
- Which has the larger context window?
- Gemini 3.5 Flash accepts more context: 1M against 400k tokens.