StepFun released Step 5 Preview, a sparse MoE model with 600B total parameters and 27B active per token, framed as "comparable intelligence at a lower unit cost."
Model and pricing
1M-token context, 64k max output, three reasoning-effort levels, text and image input (API extended to video), tool calling and JSON Schema supported. The architecture is a 92-layer narrow-deep Transformer, with gated sliding-window attention interleaved with full attention at a 3:1 ratio, and an MTP-3 speculative decoding head that accelerates end-to-end inference by about 30 percent. Each token activates 27B parameters, and FP8 inference requires a minimum of 4 B300 or 8 H200 GPUs. StepFun's API charges $1.00 per million input tokens (cache hit $0.05) and $2.70 per million output tokens (including reasoning tokens). Horizontally: GLM-5.3-Flash $0.50, DeepSeek V4.1 Flash $0.60, Step 3.7 Flash $1.15, Kimi K3 $15.00. Step 5's flagship comparison set is Kimi K3, GLM 5.3, GPT-6 Astra, and Claude Opus 5 — within the "comparable intelligence" framing, $2.70 pushes the cost curve outward by a notch.
Benchmarks and caveats
On DeepSWE v1.1, Step 5 scores 67.7, with GLM-5.3 at 66.9, Kimi K3 at 67.5, Claude Opus 5 at 74.0, and GPT-6 Astra at 74.1 — the three Chinese/open-source mid-tier models are nearly tied, trailing US flagships by 6 to 7 points. On Terminal-Bench 4.0, Step 5 lands at 33.3; on its in-house StepCodeBench, 49.0, ahead of GLM-5.3 and Kimi K3; but on real-document GDP.pdf, only 14.8, versus Astra's 31.0. StepFun itself states: Step 5 was run at High effort while rivals ran at Max (workload mismatch); six dagger-marked benchmarks include StepCodeBench and FinStepBench, both StepFun's own designs; in the HLE-with-tools row, Step 5 and GLM 5.3 are run on a text-only subset while rivals are run on the full set, and StepFun itself labels the result "not directly comparable."
Open weights and license
On October 15, three checkpoints landed on Hugging Face and ModelScope: BF16 (1,214.9 GB) and NVFP4 (394.2 GB) are downloadable directly; FP8 (650.32 GB) requires manual approval. The license is StepFun Model License 1.0, Apache-2.0 style with commercial add-ons (products above 100 million monthly active users or $20 million monthly revenue must display the Powered by StepFun AI attribution; device makers and MaaS businesses above $20 million in trailing-twelve-month revenue need a separate commercial license). The same day, DeepInfra became a second OpenRouter provider at the same price. StepFun published three 24-hour runs (H100 MLA kernel optimization reaching 508 TFLOPS, AIME24 automated post-training, and 3,000+ turns of Pokémon Red) — together they point to one thing: Step 5 is an "affordable all-day agent loop," not a single-shot Q&A model.
What it means
Step 5 Preview is "the frontier-intelligence price curve being pushed down another notch," not "yet another big model." For the open-source Chinese camp it's a reminder that the price war is not over; for US flagships it's market pressure to keep compressing per-token cost; for the self-host crowd it's 1.2 TB BF16 or 394 GB NVFP4 sitting in front of them as a real option — the threshold is high, but the license does not block the commercial path. No technical report has been published, and that is the most notable gap in this release.