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StepFun
StepFun API and models: 2 models on Impossibl, including Step 5 Preview and Step 3.7 Flash. Compare pricing per million tokens, context windows, and capabilities between different StepFun models.
models
2
modalities · in → out
takes text and image in, gives text out
latest release
Step 5 PreviewSep 20, 2026
- Step 5 Preview
stepfun/step-5-preview
Step 5 Preview is StepFun's flagship model for agentic work, aimed at software engineering and professional knowledge work with particular strength in finance.
StepFunText generationimage input
- context
- 1.02mtokens
- input price
- $1.00/1m tokens
- output price
- $2.70/1m tokens
- released
- Step 3.7 Flash
stepfun/step-3.7-flash
Step 3.7 Flash is StepFun's open-weight, high-speed multimodal reasoning model, a sparse mixture-of-experts with 198B total and 11B active parameters.
StepFunText generationimage input
- context
- 262.14ktokens
- input price
- $0.20/1m tokens
- output price
- $1.15/1m tokens
- released
compare StepFun models
compare models with the same model type and billing unit. each comparison includes published api prices, context limits, and capabilities.
frequently asked questions
Which Step models are available through Impossibl?
The directory lists 2 models from StepFun available through the Impossibl API, including Step 5 Preview and Step 3.7 Flash. Open each model page for its API identifier, capabilities, and current pricing.
How much do Step models cost?
StepFun model prices vary by model and usage. All rates below are published base API rates in USD. For token-priced models, published input rates start at $0.20 per million input tokens. Published output rates start at $1.15 per million output tokens. Input and output minima may refer to different models. Individual model pages include published cache prices and billing units. Applicable fees and workspace-specific pricing can affect the amount paid.
What is the cheapest Step model?
By published input rate, the cheapest Step text generation model on Impossibl is Step 3.7 Flash (stepfun/step-3.7-flash) at $0.20 per million input tokens and $1.15 per million output tokens. Cheapest by input rate is not always cheapest for a workload; output-heavy or cached requests can favor another model.
Does Impossibl add a markup to StepFun pricing?
No. Usage is charged at the provider's list price with 0% usage markup. Prepaid credit purchases include a 5% platform fee, and there is no subscription. The rates on this page are StepFun's published base rates, and usage comes off your balance when the request finishes.
What context windows do Step models support?
Among StepFun models with a published limit on Impossibl, the largest context window is 1,024,000 tokens, listed for Step 5 Preview. Context limits vary by model and are separate from maximum output limits.
What inputs and capabilities do Step models support?
Available model types include text generation. Published input support includes image and text; support varies by model. Tool-calling support is unspecified for 2 models.
How do I use Step models through an API?
Use the exact model identifier from the model page with the Impossibl API. For example, select stepfun/step-5-preview with /v1/chat/completions. Endpoint compatibility depends on the selected model. The API quickstart explains how to create an API key and send a request.