All tasks / Models

Step 5 Preview

StepFun's open-weights flagship MoE with 600B total and 27B active parameters, 1M-token context.

StepFun
Open weights
Released 20 Sep 2026

Where it ranks

A
Chat & assistants
Models · Local · 1,447 on LMArena Text Arena (overall, style control)
B
Writing
Models · Local · 1,403 on LMArena Text Arena: Creative Writing (style control)
C
Coding
Models · Local · 1,565 on LMArena WebDev / Code Arena (overall)
A
Image understanding
Models · Local · 1,250 on LMArena Vision Arena (overall, style control)
C
Workflow automation
Models · Local · 51% on AutomationBench-AA (Artificial Analysis)

Facts

Vendor: StepFun
Family: Step
Released: 20 Sep 2026
Weights: Open: download and run it yourself
License: StepFun Model License 1.0
Parameters: 604B (27B active)
GPU memory to run locally: ~346 GB (4-bit ≈ 604 B × 0.57 GB + 1.5 GB ≈ 346 GB, estimate.)
API price: $1 in / $2.7 out per 1M tokens (OpenRouter listed price)
Access: Free (open weights)
Last verified: 19 Oct 2026

Price from openrouter.ai, 19 Oct 2026.

Benchmark results

Benchmark	Result	Entry on the leaderboard	As of	Source
Artificial Analysis Intelligence Index	44	`Step 5 Preview` Raw value from the page's embedded model data; the site displays it rounded to an integer.	19 Oct 2026	artificialanalysis.ai
Artificial Analysis MMMU-Pro (independent evaluation)	76.4%	`Step 5 Preview` Raw fraction 0.7636 from the model data embedded in https://artificialanalysis.ai/leaderboards/models, converted to percent; rank 45 of 124 entries with an MMMU-Pro result; no last-updated date shown.	19 Oct 2026	artificialanalysis.ai
AutomationBench-AA (Artificial Analysis)	51%	`Step 5 Preview` AutomationBench-AA Score (share of each task's objectives completed, a task with any guardrail violation scoring zero); raw value from the page's embedded model data (displayed rounded); rank 25 of 32; Tasks Completed 17.66%, Objectives Completed 78.52%; no last-updated date shown, so as_of = retrieval date.	19 Oct 2026	artificialanalysis.ai
LMArena Text Arena (overall, style control)	1,447	`Step 5 Preview` From LMArena's official leaderboard-dataset (text_style_control, split latest, category overall, published 2026-10-15), which mirrors https://arena.ai/leaderboard/text. Rank 84; 7116 votes; 95% CI 1439.8-1454.8.	15 Oct 2026	huggingface.co
LMArena Text Arena: Creative Writing (style control)	1,403	`Step 5 Preview` From LMArena's official leaderboard-dataset (text_style_control, split latest, category creative_writing, published 2026-10-15), which mirrors https://arena.ai/leaderboard/text/creative-writing. Rank 104 of 414; 1517 votes; 95% CI 1387.2-1419.2.	15 Oct 2026	huggingface.co
LMArena Vision Arena (overall, style control)	1,250	`Step 5 Preview` From LMArena's official leaderboard-dataset (vision_style_control, split latest, category overall, published 2026-10-09), which mirrors https://arena.ai/leaderboard/vision. Rank 55 of 165; 1088 votes; 95% CI 1232.1-1268.4.	9 Oct 2026	huggingface.co
LMArena WebDev / Code Arena (overall)	1,565	`Step 5 Preview (High)` From LMArena's official leaderboard-dataset (webdev = Code Arena, split latest, category overall, published 2026-10-18), which mirrors https://arena.ai/leaderboard/webdev. Rank 37; 4603 votes; 95% CI 1555.6-1575.4.	18 Oct 2026	huggingface.co

Where you can use it

SOpenRouterRuntimes & gateways · Cloud

Earlier versions

Step 3.5 Flash · —

Compare

Alternatives to Step 5 Preview

Sources