This model is no longer available.
Model Card
Step3 is a multimodal reasoning model from StepFun, built on a Mixture-of-Experts architecture with 321B total parameters and 38B active per token. It accepts both text and image inputs, making it suitable for vision-language tasks.
The model is engineered for cost-effective decoding through two co-designed innovations: Multi-Matrix Factorization Attention (MFA) to reduce KV cache size, and Attention-FFN Disaggregation (AFD) for more efficient distributed inference. StepFun reports it achieves significantly higher tokens-per-GPU throughput than DeepSeek-V3 at comparable context lengths.
Step3 targets use cases that require grounded multimodal reasoning — interpreting diagrams, documents, and images alongside text — with reduced hallucination.
Context Window N/A
tokens
Max Output 66K
tokens
Input Cost $0.57
per million tokens
Output Cost $1.42
per million tokens
Release Date Jul 28, 2025
API Usage Example
Add AI to your app with just a few lines of code.
No backend, no configuration required.
// npm install @heyputer/puter.js
import { puter } from '@heyputer/puter.js';
puter.ai.chat("Explain quantum computing in simple terms").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").then(response => {
document.body.innerHTML = response.message.content;
});
</script>
</body>
</html>
# pip install openai
from openai import OpenAI
client = OpenAI(
base_url="https://api.puter.com/puterai/openai/v1/",
api_key="YOUR_PUTER_AUTH_TOKEN",
)
response = client.chat.completions.create(
model="MODEL_ID",
messages=[
{"role": "user", "content": "Explain quantum computing in simple terms"}
],
)
print(response.choices[0].message.content)
curl https://api.puter.com/puterai/openai/v1/chat/completions \
-H "Content-Type: application/json" \
-H "Authorization: Bearer YOUR_PUTER_AUTH_TOKEN" \
-d '{
"model": "MODEL_ID",
"messages": [
{"role": "user", "content": "Explain quantum computing in simple terms"}
]
}'
More AI Models From StepFun
Frequently Asked Questions
You can access Step3 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.
Yes, it is free if you're using it through Puter.js. With the User-Pays Model, you can add Step3 to your app at no cost — your users pay for their own AI usage directly, making it completely free for you as a developer.
| Price per 1M tokens | |
|---|---|
| Input | $0.57 |
| Output | $1.42 |
Step3 was created by StepFun and released on Jul 28, 2025.
Step3 can generate up to 66K tokens in a single response.
Yes — the Step3 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.
Get started with Puter.js
Add AI to your application without worrying about API keys or setup.
Explore Models View Tutorials