StepFun

Introducing Step 5 Preview: Advancing the Pareto Frontier. Step 5 Preview is our new flagship model for agentic work, delivering frontier-level performance across software engineering and professional knowledge work, with particular strength in finance. - 600B total / 27B active MoE, with 1M context + Vision - Substantially lower task cost at comparable intelligence - Broad software engineering capabilities with sustained execution over long horizons Try Step 5 Preview: https://platform.stepfun.ai Model page: https://www.stepfun.com/step-5-preview Open weights on Oct 15.

StepFun and ACE Studio present StepAudio 3 Music, StepFun’s first music generation foundation model — built to turn a prompt and lyrics into a complete song. Describe the sound you want: • Genre, mood and vocal character • Instruments, key and BPM • Song structure and arrangement Four workflows in one model: 🎤 Song generation 🎹 Instrumental generation 🔁 Music cover 🎙️ Vocal-to-song arrangement Powered by ABC-COT, it plans musical structure and arrangement before synthesis. Generate a version, rewrite the prompt, edit the ABC notation, and iterate toward the sound in your head. (ABC-COT API coming soon) Try the interactive demo: › https://static.stepfun.com/blog/stepaudio3/music/

Introducing Step Code v0.1.0. Swift execution. High token efficiency. Long-horizon reliability. Now open source under the MIT License. Step Code handles the full development loop—from reading and editing code to running tests and shipping—from one CLI. - 80.9% on Terminal-Bench 2.1 in evaluation - 73.3% on Multi-Frame, our 150-task long-horizon benchmark - One-command static site publishing with StepPage GitHub: https://github.com/stepfun-ai/Step-Code

Introducing StepAudio 3, our new family of 5 audio models for real-time voice, speech recognition, speech generation, audio generation and music. Realtime ranks #1 on Artificial Analysis for both Conversational Dynamics (98.9%) and Speech Reasoning (99.7%). ASR reaches 1.7% WER, matching the best result on the leaderboard. Build voice agents that handle interruptions, reason while speaking, and call tools. Transcribe speech, generate expressive voices, and create full audio scenes and music. Available now: Voice AI Lab: https://audio.stepfun.ai/ Blog: https://static.stepfun.com/blog/stepaudio3/

We’ve open-sourced onPanda 🐼 — the tool we use internally for LLM data annotation and model inspection. The workflow is simple: find an error, correct the token, and let the model continue. ✍️ Data annotation - 52% lower median annotation time vs. manual post-editing - SFT + preference data in one workflow, with high on-policy fidelity (ΔPPL <1% vs. the model’s resampling baseline) - Precise token-level supervision with paired positive/negative examples, plus agent-trajectory annotation across image, audio, and video 🔎 Model inspection and debugging - Inspect token probabilities and top-k alternatives, steer decoding token by token, and explore SVG generation, web development, and agent tasks directly in the browser. Try it (mobile-friendly): https://onpanda.diyer22.com Paper: https://huggingface.co/papers/2609.24983

Step 5 Preview pushes our intelligence–cost Pareto frontier outward. It comes in at 44 on the Artificial Analysis Intelligence Index, $0.71 per task. Thanks @ArtificialAnlys for putting Step 5 Preview through the full evaluation. More to come on Oct 15.

That’s a wrap on AGNTCon + MCPCon Japan. Two days of meeting AI builders, exchanging ideas on agent infrastructure, and seeing what people are building across the ecosystem. We are especially excited to see several great agent infrastructure projects joining the StepFun Startup Program. Building with AI? We’d love to support what you’re working on: https://platform.stepfun.ai/startup-program Next stop: San Jose for AGNTCon + MCPCon North America with @AgenticAIFdn (AAIF). More updates from StepFun are coming soon. Stay tuned!

Step 5 Preview is now on @OpenRouter's New & Trending leaderboard. Thanks to everyone giving it a try, and to our partners bringing it into your workflow.

We’re bringing StepAudio 3 to San Francisco this Wednesday. Live demos, an open AMA with the StepAudio team, and a panel with leaders from http://PLAUD.AI, Cresta, Coval, SGLang-Omni & StepFun on what works, what still breaks in production, and where real-time AI interaction is heading next. 📍 Sep 16 · SF 🎁 $100 API credits + drinks & light dinner Join us ↓ https://luma.com/bkpe5h92

One week since launch, Step 5 Preview is already #2 on OpenRouter's weekly leaderboard, with 19.5T tokens used. It has also held #2 on the daily leaderboard since Oct 10. Thanks to everyone building with us.

Rain couldn't stop the builders. Great conversations at our Step 5 Preview Launch Night with @togethercompute! From long-horizon agents and tool-calling reliability to inference costs and what AI breakthroughs mean for the next wave of startups. Huge thanks to our panelist Dan Fu (@realDanFu · @togethercompute), Mar Hershenson (@MarHershenson · @pearvc), Saoud Rizwan (@sdrzn · @cline), and Joey Wang (@harvey), and everyone who joined us! More to come.

Step 5 Preview now exists where you build. Now live on @OpenRouter. A week of free access is rolling out today across @opencode, @cline , @NousResearch, @kilocode, and more. Flagship-tier intelligence for agentic and professional work, at substantially lower task cost. Keep your workflow. Switch your model. Try Step 5 Preview on OpenRouter: https://openrouter.ai/stepfun/step-5-preview