Step 3.5
#132 in Frontier LLMsstepfun · v3.5 · since 2026-02-02 · 3× · last seen Jun 29, 2026
9
Momentum
Step 3.5 Flash is an open-weight reasoning model by StepFun built on a sparse Mixture-of-Experts architecture, activating only 11B of its 196B total parameters per token. The model is purpose-built for coding and agentic tasks and supports a 256K-token context window. It is a text-only model without image or video modality and is released under the Apache 2.0 license. The API is accessible via the StepFun platform as well as third-party providers such as OpenRouter.
Momentum trend
04.04.03.07.
Features
| Coding Benchmark (SWE-bench Pro %) | 74.4% on SWE-bench Verified; 51.3% on SWE-bench Pro (per comparison data for successor version Step 3.7 Flash) |
| Context Window (Tokens) | 256,000 tokens (256K) per official documentation; 262,144 tokens (262K) per OpenRouter API listing |
| Multimodal (Image/Video) | No – text-only; no image or video input supported |
| NLP Benchmark Score | AIME 2025: 97.3%; LiveCodeBench v6: 86.4%; τ²-Bench: 88.2%; IMO-AnswerBench: 85.4% |
| Price per 1M Input Tokens | $0.09 (via OpenRouter) or $0.10 (via StepFun directly) |
| Price Tier (Monthly) | No monthly subscription model; pure pay-per-use API. OpenRouter also offers a free trial access. |