Step 3.7 Flash

Step 3.7 Flash is a 198B-parameter sparse Mixture-of-Experts vision-language model released by StepFun AI on May 29, 2026. Despite its massive total parameter count, it activates only ~11B parameters per token through expert routing (8 out of 288 experts), delivering near-frontier intelligence at inference costs comparable to small dense models. The model combines a 196B language backbone with a 1.8B native vision encoder, supports a 256K context window, and achieves up to 400 tokens/second throughput on cloud APIs.

The model's primary differentiation lies in agentic workflow reliability rather than absolute intelligence ceiling. It leads the ClawEval-1.1 benchmark at 67.1 (a 23.5-point jump over its predecessor Step 3.5 Flash) and places second on SWE-Bench PRO at 56.3. Its most innovative feature is Advisor Mode, a two-tier execution strategy where Step 3.7 Flash handles routine tool-calling and iteration while escalating to a larger frontier model only at genuine decision points, achieving approximately 97% of Claude Opus 4.6's coding performance at roughly one-ninth the per-task cost ($0.19 vs $1.76).

The model is fully open-weight under Apache 2.0 and ships with quantized checkpoints (BF16, FP8, NVFP4, GGUF) across HuggingFace, enabling local deployment on 128GB+ unified memory devices like NVIDIA DGX Spark and Mac Studio. It is available via StepFun's own platform, OpenRouter, NVIDIA NIM, and forthcoming partnerships with DeepInfra, Fireworks AI, and Modal. Where it falls short is on pure reasoning benchmarks (HLE w/ tools at 47.2% vs Claude Opus 4.7's 54.7%), terminal-heavy workflows (Terminal-Bench 2.1 at 59.5 vs GPT 5.5's 82.7), and general professional tasks (GDPVal-AA at 45.8% vs frontier models at 63%).