step-3-5-flash
Step 3.5 Flash is StepFun’s most capable open-source foundation model, a sparse mixture-of-experts that activates only 11B of its 196B parameters per token.
Precio: Entrada: 24 créditos / 1 M de tokens (≈ $0.12); salida: 72 créditos / 1 M de tokens (≈ $0.36).
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Step 3.5 Flash API on ModelFold
Step 3.5 Flash is StepFun’s most capable open-source foundation model, a sparse mixture-of-experts that activates only 11B of its 196B parameters per token. Try Step 3.5 Flash in the ModelFold Playground, then call it from your own code through an OpenAI-compatible chat completions API.
What Is the Step 3.5 Flash API
Step 3.5 Flash at a glance
Step 3.5 Flash is a chat model from StepFun. It accepts text as input and returns text, with a context window of up to 262K tokens.
Use it without hosting anything
On ModelFold you call Step 3.5 Flash with a single API key — no model weights to download and no inference servers to run. The same key also works for the other chat, image, video and audio models on ModelFold.
Core Capabilities of Step 3.5 Flash
Up to 262K tokens of context
Keep long conversations, large documents and sizeable code in a single request, so the model can reason over the full material instead of fragments.
Function calling
Step 3.5 Flash supports tool (function) calling: describe your functions in the request and the model returns structured calls your code can run — the basis for agents and integrations.
Reasoning mode
Step 3.5 Flash can produce reasoning before its final answer; in the Playground you can switch reasoning on or off to compare results.
How to Use Step 3.5 Flash on ModelFold
- 1
Step 1: Try it in the Playground
Open the Playground at the top of this page, type a prompt and see how Step 3.5 Flash responds before writing any code.
- 2
Step 2: Create an API key
Sign in to ModelFold and create an API key in the console. Keep it secret and send it as a Bearer token.
- 3
Step 3: Send a request
Call POST https://modelfold.ai/v1/chat/completions with "model": "step-3-5-flash" and your messages. Existing OpenAI-compatible SDKs work by changing the base URL and key.
- ✓
Step 4: Ship and monitor
Integrate the response into your product and check token usage and spend for every call in the console logs.
What You Can Build with Step 3.5 Flash
High-volume pipelines
Run classification, extraction, rewriting and batch jobs at scale where cost per request matters.
Analysis and complex reasoning
Work through research questions, data interpretation, planning and other problems that need careful step-by-step reasoning.
Autonomous agents
Build agents that plan multi-step tasks, call your tools and APIs, and keep working toward a goal across long sessions.
AI coding assistants
Generate, explain, debug and refactor code, review pull requests and work through multi-file changes in developer tools and IDE plugins.
Frequently Asked Questions
What is Step 3.5 Flash?⌄
Step 3.5 Flash is StepFun’s most capable open-source foundation model, a sparse mixture-of-experts that activates only 11B of its 196B parameters per token.
Which inputs does Step 3.5 Flash support?⌄
Step 3.5 Flash accepts text and returns text. Through ModelFold you send text messages; documents attached in the Playground are converted to text.
How long is the context window of Step 3.5 Flash?⌄
Up to 262K tokens, shared between your input and the model’s output.
Does Step 3.5 Flash support function calling?⌄
Yes. Step 3.5 Flash supports tools / function calling through the standard tools parameter of the chat completions API.
How is Step 3.5 Flash billed on ModelFold?⌄
Pay as you go by tokens: input and output tokens are charged at the per-million-token prices shown on this page. There is no monthly fee, and failed requests are not charged.
How do I call Step 3.5 Flash through the API?⌄
Send a POST request to https://modelfold.ai/v1/chat/completions with "model": "step-3-5-flash", using your ModelFold API key as the Bearer token.
| Entrada | 24 créditos 1M tokens≈ $0.12 |
| Salida | 72 créditos 1M tokens≈ $0.36 |
Se cobra por token, con tarifas separadas para entrada y salida. Los tokens de razonamiento cuentan como salida. El entorno de pruebas aplica exactamente el mismo cálculo.
Leer la documentación de la API →AI Agents · Claude Code / Cursor / Trae →curl https://modelfold.ai/v1/chat/completions \
-H "Authorization: Bearer $MODELFOLD_API_KEY" \
-H "Content-Type: application/json" \
-d '{"model":"step-3-5-flash","messages":[{"role":"user","content":"Hello"}]}'