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Step-3.5-Flash
Step-3.5-Flash is an open-weight model from StepFun, released Jan 29, 2026. It ranks #151 of 351 on the LMArena text leaderboard with a rating of 1403. It costs $0.10 per million input tokens and $0.30 per million output tokens, with a 256K-token context window.
- Developer
- StepFun
- Released
- Jan 29, 2026
- Context window
- 256K
- Price in / out, per 1M tokens
- $0.10 / $0.30
- Weights
- Open · Apache 2.0
- Inputs
- Text
- Reasoning
- Yes
- Tool use
- Yes
- Hugging Face downloads, 30 days
- 265.3K
- Hugging Face likes
- 844
The rating LMArena published at each update since Feb 6, 2026. Ratings move as votes come in and new models join.
LMArena, by category
| Leaderboard | Rating | Rank | Votes |
|---|---|---|---|
| TextLMArena | 1403 | 151 / 351 | 60.3K |
| CodingLMArena | 1436 | 129 / 346 | 15.2K |
| MathLMArena | 1408 | 149 / 339 | 3.4K |
| Creative writingLMArena | 1357 | 160 / 349 | 9.8K |
| Instruction followingLMArena | 1385 | 152 / 351 | 19.3K |
| Hard promptsLMArena | 1411 | 149 / 351 | 37.5K |
| Multi-turnLMArena | 1405 | 147 / 349 | 10.4K |
| Long queriesLMArena | 1402 | 146 / 330 | 22.8K |
| ExpertLMArena | 1422 | 134 / 305 | 5.3K |
| Legal and governmentIndustries | 1408 | 148 / 325 | 4.7K |
| Medicine and healthcareIndustries | 1409 | 151 / 325 | 4.2K |
| Business and financeIndustries | 1394 | 151 / 344 | 11.8K |
| ChineseLanguages | 1446 | 134 / 328 | 3.7K |
| SpanishLanguages | 1419 | 117 / 249 | 2K |
| GermanLanguages | 1405 | 120 / 261 | 1.1K |
| FrenchLanguages | 1421 | 132 / 252 | 2K |
| JapaneseLanguages | 1353 | 124 / 236 | 679 |
LMArena, CC BY 4.0, as of Oct 22, 2026. Where a model is rated at several effort levels, its best is shown.
Compare Step-3.5-Flash
StepFun
Builds the Step family of large multimodal models. Founded 2023, based in Shanghai. stepfun.com
Questions
Who makes Step-3.5-Flash?
Step-3.5-Flash is made by StepFun, founded 2023 and based in Shanghai.
How much does Step-3.5-Flash cost?
$0.10 per million input tokens and $0.30 per million output tokens, at its provider’s list price.
What is Step-3.5-Flash’s context window?
256K tokens (262,144).
How does Step-3.5-Flash rank?
#151 of 351 on LMArena’s text leaderboard, rated 1403 (95% interval 1399–1406) from 60,329 votes, as of Oct 22, 2026.
Is Step-3.5-Flash open source?
Step-3.5-Flash has open weights under the Apache 2.0 license, downloadable from Hugging Face (stepfun-ai/Step-3.5-Flash).