Step 5 Preview from @StepFun_ai hit #1 on OpenRouter Trending, a day after launch.
It's available in Kilo Code, Cline, Hermes Agent, and OpenCode. Keep your workflow and just switch models.
I've tested the model.
It’s a great model and has some nice properties.
I've been using it as a coding agent since early access.
It checks its own work and stops when the task is done. I would use it for long agent runs that I don't watch closely.
StepFun built it for real engineering work. That covers fixing bugs in unfamiliar codebases, implementing features across files, and refactoring, with changes that run and pass checks.
Frontend is the other big focus. You can give it a screenshot, a mockup, or a PRD, and it can return a working web page. It can also build a playable browser game from a set of assets.
Beyond code, it reads annual reports and operating data and turns them into financial reports, editable spreadsheets, and slide decks.
The context window is 1M tokens, with up to 1M output tokens. That is enough for large codebases and long multi-step tasks.
Under the hood, Step 5 Preview is a sparse MoE with 600B total parameters and 27B active per token.
Open weights are coming on Oct 15. Very much looking forward to its release.