StepFun: Step 5 Preview
stepfun/step-5-preview
Try Step 5 Preview for free in your browser, and add it to your app for free with Puter.js AI API.
Try it free Add to your app// npm install @heyputer/puter.js
import { puter } from '@heyputer/puter.js';
puter.ai.chat("Explain quantum computing in simple terms", {
model: "stepfun/step-5-preview"
}).then(response => {
document.body.innerHTML = response.message.content;
});
<html>
<body>
<script src="https://js.puter.com/v2/"></script>
<script>
puter.ai.chat("Explain quantum computing in simple terms", {
model: "stepfun/step-5-preview"
}).then(response => {
document.body.innerHTML = response.message.content;
});
</script>
</body>
</html>
Model Card
Step 5 Preview is a preview release of StepFun's next flagship chat model, served through the API with a 1M-token context window and up to 64K output tokens.
The model supports tool calling and adjustable reasoning effort (low, medium, high), and StepFun positions it for agentic coding, software engineering, long-context work with repeated tool calls, and professional knowledge tasks.
It suits developers building coding agents or multi-step tool-using pipelines that need to keep large codebases or documents in context.
Context Window 1M
tokens
Max Output 64K
tokens
Input Cost $1
per million tokens
Output Cost $2.7
per million tokens
Release Date Oct 8, 2026
Try Step 5 Preview for free
Try Step 5 Preview instantly in your browser.
This playground uses the Puter.js AI API — no API keys or setup required.
More AI Models From StepFun
Step 3.7 Flash
Step 3.7 Flash is a multimodal Mixture-of-Experts model from StepFun, combining a 196B-parameter language backbone with a 1.8B vision encoder and activating roughly 11B parameters per token. It natively processes text and images, supporting a 256K-token context window. The model is designed for agentic coding, tool orchestration, long-context reasoning, and search-intensive workflows. It exposes tunable reasoning tiers (low, medium, high) so developers can trade inference cost against answer depth on a per-call basis. Compared to Step 3.5 Flash, Step 3.7 Flash adds native vision input, improves cross-harness consistency, and achieves stronger performance on coding agent and terminal benchmarks. It targets developers building production pipelines that combine perception, retrieval, and multi-step execution.
ChatStep 3.5 Flash
Step 3.5 Flash is an open-source reasoning model from StepFun, built on a sparse Mixture-of-Experts (MoE) architecture with 196B total parameters but only 11B active per token. It supports a 256K-token context window and native tool calling. The model is purpose-built for agentic and coding workflows, with generation throughput of 100–300 tokens/sec in typical usage. It scores 74.4% on SWE-bench Verified, 97.3 on AIME 2025, 86.4% on LiveCodeBench-V6, and 88.2 on τ²-Bench. Step 3.5 Flash is a strong choice for developers building AI agents, code assistants, or multi-step reasoning pipelines who need frontier-level intelligence at low per-token cost.
Frequently Asked Questions
You can access Step 5 Preview by StepFun through Puter.js AI API. Include the library in your web app or Node.js project and start making calls with just a few lines of JavaScript — no backend and no configuration required. You can also use it with Python or cURL via Puter's OpenAI-compatible API.
Step 5 Preview is free to try with a Puter account. Every account includes a free AI allowance, and you can chat with it in the playground on this page. You can upgrade your account anytime for a larger allowance.
Step 5 Preview is free to integrate using the Puter.js AI API. With the User-Pays Model, you can add AI to your app for $0, since users cover their own AI usage through their Puter account.
| Price per 1M tokens | |
|---|---|
| Input | $1 |
| Output | $2.7 |
Step 5 Preview was created by StepFun and released on Oct 8, 2026.
Step 5 Preview supports a context window of 1M tokens. For reference, that is roughly equivalent to 2,000 pages of text.
Step 5 Preview can generate up to 64K tokens in a single response.
Yes — the Step 5 Preview API works with any JavaScript framework, Node.js, or plain HTML through Puter.js. Just include the library and start building. See the documentation for more details.
Add Step 5 Preview to your app for free
Developers can integrate Step 5 Preview for free using the Puter.js AI API.
With the User-Pays Model, each user covers their own AI usage instead of the developer.