Step 5 Preview
StepFun's Step 5 Preview is a very large text model for writing and answering questions, offered to developers and not free to download.
Key facts
- Released
- Sep 18, 2026
- What it does
- Text and chat: Writes, answers questions and holds a conversation.Thinks first: Can reason step by step before it answers: slower, but better at maths, code and tricky questions.Sees images: Understands pictures, screenshots and charts you share with it.Watches video: Understands video clips you share with it.
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- How
- For developers, through an API
- Size
- Parameters: The numbers a model learns during training: a rough measure of its size. Bigger usually means more capable, but slower and pricier to run. 7B means 7 billion.
From trckr's archive of releases before it started watching. Date and details from Epoch AI's database of AI models (CC BY 4.0).
Price and limits
What developers pay to use it through the API: How developers plug a model into their own apps and pay per use. A model that's "in the API" can be used by programmers, even if it isn't in a chat app yet., per million Tokens: The small chunks of text a model reads and writes, about three-quarters of a word each. Prices and limits are counted in tokens. sent (input) or written back (output), and how much it can take in at once.
- Input
- $1.05
- per million tokensCached: $0.105
- Output
- $2.99
- per million tokens
- Context window: How much a model can keep in mind at once: your question, any files you share and its own replies. Measured in tokens; 1,000 tokens is about 750 words.
- 1M tokens
- about 750,000 words
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- Longest answer
- 66K tokens (about 49,000 words)
From the lab's own listing on models.dev and OpenRouter, checked .
How it scores
From independent testers, never the lab's own claims.
- Chat answers, by people's votes#70 of 86
- Gemini 4 Carbon1,527
- 2Gemini 4 Argon1,522
- 69ERNIE-5.0-Preview1,449
- 70Step 5 Preview1,448
- 71MiMo-V2-Pro1,448
Source: LMArena · LMArena text, adjusted for style
- Building apps, by people's votes#39 of 85
- Claude Opus 5.51,818
- 2Claude Sonnet 5.51,773
- 38GPT-6 Luna1,577
- 39Step 5 Preview1,572
- 40Mistral Large 41,563
Source: LMArena · LMArena WebDev
Compare Step 5 Preview with
It came out 113 days after Step 3.7 Flash, the lab's previous model.
The details
Step 5 Preview: An early version released for testing. It may change or disappear, and is often limited while it lasts. is StepFun's 600 billion parameters: Data-centre scale: it runs on many chips (GPUs) at once. Parameters are the numbers a model learns: a rough measure of its size. Language model (LLM): A model trained on huge amounts of text to read and write. The engine behind chatbots like ChatGPT, Claude and Gemini. for text generation and question answering, released via API: How developers plug a model into their own apps and pay per use. A model that's "in the API" can be used by programmers, even if it isn't in a chat app yet. access only.
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