One-line summary
On October 15, 2026, StepFun announced that its new flagship foundation model Step 5 Preview is now fully open-sourced with complete model weights and third-party interfaces. First unveiled on September 20, 2026, the model targets AI coding, software engineering, knowledge work and finance, natively supports text, image and video input, and offers a 1M-token context window.
Event Overview
According to CNMO's report on October 15, 2026, StepFun announced that day that Step 5 Preview, its new flagship foundation model, is now fully open-sourced with complete weights, and that the model has opened third-party interfaces across the board. StepFun first unveiled the model on September 20, 2026, positioning it as a flagship foundation model for real-world tasks, focused on coding and knowledge work, aiming to improve performance on real-world agentic tasks. The open weights are listed on ModelScope as stepfun-ai/Step-5-Preview-BF16.
Key Information
| Item | Detail |
|---|---|
| Open-source date | October 15, 2026 |
| First unveiling | September 20, 2026 |
| Publisher | StepFun |
| Model | Step 5 Preview, new flagship foundation model |
| Target scenarios | AI coding, software engineering, knowledge work, finance |
| Input capability | Native text, image and video input (per StepFun platform docs) |
| Context | 1M-token context window (per StepFun platform docs) |
| Open-source channel | ModelScope: stepfun-ai/Step-5-Preview-BF16; third-party interfaces opened |