Step 5 Preview, the StepFun model in numbers

What you need to know

StepFun released Step 5 Preview on September 16, 2026. It has a reasoning mode: it can "think" before answering, which helps with multi-step problems but uses more tokens, and therefore more money. Its weights are published: you can download it and run it on your own servers, or use one of the 19 API providers that list it on models.dev. It is a very recent release.

We file it under open-weight models (68 models in this category on the site).

Benchmark results

As of October 22, 2026, Epoch AI publishes no score for Step 5 Preview on our basket's benchmarks. To place it, rely on its specifications and price, then test it on your own cases.

Pricing and budget

Step 5 Preview costs $1.05 per million input tokens and $2.99 per million output tokens (developer's price, checked on October 22, 2026).

To put it in perspective: reading 20,000 tokens (about thirty pages) and writing 2,000 costs roughly $0.027; a thousand of those tasks, $26.9.

That is 3 times the median output price of open-weight models ($1).

Tokens read back from cache cost $0.10 per million, which helps an agent that keeps resending the same context.

To estimate your own budget, use the agent cost calculator.

Technical specifications

Its context window reaches 1,000,000 tokens, roughly 1,500 pages of text at 500 words per page: enough to load a whole book or a mid-sized codebase. A single answer can run to 65,536 tokens.

It accepts as input: text, image and video.

It can call tools (functions, APIs) and return structured JSON output, which makes it a possible foundation for an AI agent.

The weights are published on Hugging Face (stepfun-ai/Step-5-Preview). See also our list of open-source models.

What is it good for?

Given its category, Step 5 Preview is mainly aimed at projects where you want control over your data or hosting, or want to adapt the model to your field.

Its very large context window makes it worth considering for analysing large sets of documents in a single request.

Before adopting it, test it on your own examples: benchmarks measure standard tasks, not your job.

Comparable models

In the same category, the models closest to Step 5 Preview are:

• Hermes 4 405B (Nous Research, $2.99 per million output tokens)
• Kimi K2.5 (Moonshot AI, index 78.1)
• Qwen3.6 27B (Alibaba Cloud (Qwen), index 72.2)
• GLM-5 (Zhipu AI (Z.ai), index 77.2)