Model comparison
GPT-5.5 Pro vs Step 3.5 Flash
GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 41.7 on the Noometry Index. Step 3.5 Flash costs 450× less per token, which makes it the better buy when GPT-5.5 Pro's lead doesn't matter for your workload.
Last verified . 0 shared benchmarks.
StepFunSummary
- The widest gap is in reasoning, where GPT-5.5 Pro leads 73.6 to 21.2.
- Step 3.5 Flash is cheaper at $0.10 / $0.30 per million input/output tokens, against $30 / $180 for GPT-5.5 Pro.
- GPT-5.5 Pro accepts more context: 1.05M tokens versus 256K.
- Step 3.5 Flash has downloadable open weights; the other is API-only.
Side by side
| GPT-5.5 Pro | Step 3.5 Flash | |
|---|---|---|
| Provider | OpenAI | StepFun |
| Noometry Index | 64.3 | 41.7 |
| Released | 2026-04-23 | 2026-01-29 |
| Weights | Proprietary | Open |
| Context window | 1.05M | 256K |
| Max output | 128K | 256K |
| Input $ / M tokens | $30 | $0.10 |
| Output $ / M tokens | $180 | $0.30 |
| Results tracked | 14 | 19 |
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Category by category
Coding Not comparable
GPT-5.5 Pro: —, Step 3.5 Flash: 41.7 (#106)
| Benchmark | GPT-5.5 Pro | Step 3.5 Flash |
|---|---|---|
| LMArena Coding | — | 1436 |
Reasoning GPT-5.5 Pro leads
GPT-5.5 Pro: 73.6 (#7), Step 3.5 Flash: 21.2 (#202)
| Benchmark | GPT-5.5 Pro | Step 3.5 Flash |
|---|---|---|
| ARC-AGI-2 | 84.6% | — |
| SimpleBench | 76.9% | — |
| NYT Connections (extended) | — | 28.4% |
| ARC-AGI-1 | 96.5% | — |
| CritPt | 30.6% | — |
| Chess Puzzles | 64% | — |
| LMArena Hard Prompts | — | 1411 |
| DTBench | 96% | — |
| LMCA | 53.9% | — |
| Epoch Capabilities Index | 162.45 | — |
Math GPT-5.5 Pro leads
GPT-5.5 Pro: 83.8 (#8), Step 3.5 Flash: 40.6 (#77)
| Benchmark | GPT-5.5 Pro | Step 3.5 Flash |
|---|---|---|
| FrontierMath (Tiers 1-3) | 87.7% | — |
| FrontierMath Tier 4 | 78% | — |
| MathArena Final-Answer Competitions | — | 66.8% |
| OTIS Mock AIME 2024-2025 | 100% | — |
| LMArena Math | — | 1408 |
| FrontierMath (Feb 2025 set) | 52.4% | — |
| FrontierMath Tier 4 (v1) | 39.6% | — |
Knowledge GPT-5.5 Pro leads
GPT-5.5 Pro: 64.2 (#17), Step 3.5 Flash: 39.0 (#127)
| Benchmark | GPT-5.5 Pro | Step 3.5 Flash |
|---|---|---|
| GPQA Diamond | 93.9% | — |
| LMArena Expert | — | 1422 |
Multilingual Not comparable
GPT-5.5 Pro: —, Step 3.5 Flash: 50.7 (#115)
| Benchmark | GPT-5.5 Pro | Step 3.5 Flash |
|---|---|---|
| LMArena Non-English | — | 1386 |
| LMArena Chinese | — | 1448 |
| LMArena French | — | 1421 |
| LMArena German | — | 1404 |
| LMArena Japanese | — | 1353 |
| LMArena Korean | — | 1350 |
| LMArena Russian | — | 1385 |
| LMArena Spanish | — | 1419 |
Instruction Following Not comparable
GPT-5.5 Pro: —, Step 3.5 Flash: 73.3 (#119)
| Benchmark | GPT-5.5 Pro | Step 3.5 Flash |
|---|---|---|
| LMArena Instruction Following | — | 1385 |
Long Context Not comparable
GPT-5.5 Pro: —, Step 3.5 Flash: 42.8 (#112)
| Benchmark | GPT-5.5 Pro | Step 3.5 Flash |
|---|---|---|
| LMArena Longer Query | — | 1402 |
Writing & Preference Not comparable
GPT-5.5 Pro: —, Step 3.5 Flash: 59.0 (#108)
| Benchmark | GPT-5.5 Pro | Step 3.5 Flash |
|---|---|---|
| LMArena Text | — | 1403 |
| LMArena Creative Writing | — | 1357 |
| LMArena Multi-Turn | — | 1405 |
Frequently asked questions
Is GPT-5.5 Pro better than Step 3.5 Flash?
GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 41.7 on the Noometry Index. Step 3.5 Flash costs 450× less per token, which makes it the better buy when GPT-5.5 Pro's lead doesn't matter for your workload.
Which is cheaper, GPT-5.5 Pro or Step 3.5 Flash?
Step 3.5 Flash is cheaper. It lists at $0.10 per million input tokens and $0.30 per million output tokens; GPT-5.5 Pro lists at $30 and $180.
Which has the bigger context window?
GPT-5.5 Pro does, with 1.05M tokens against 256K.
How many benchmarks do GPT-5.5 Pro and Step 3.5 Flash share?
0 benchmarks have published results for both models. GPT-5.5 Pro has 14 scored results on Noometry and Step 3.5 Flash has 19.