StepFun 3.5 Flash
Step 3.5 Flash is an open-source reasoning model by StepFun with 196B total parameters (11B active) using Mixture of Experts. It features a 256K context window, deep reasoning, tool calling, and agentic capabilities, achieving 97.3 on AIME 2025 and 74.4% on SWE-bench Verified.
import { streamText } from 'ai'
const result = streamText({ model: 'stepfun/step-3.5-flash', prompt: 'Why is the sky blue?'})Playground
Try out StepFun 3.5 Flash by StepFun. Usage is billed to your team at API rates. Free users (those who haven't made a payment) get $5 of credits every 30 days.
Providers
Route requests across multiple providers. Copy a provider slug to set your preference. Visit the docs for more info. Using a provider means you agree to their terms, listed under Legal.
P50 throughput on live AI Gateway traffic, in tokens per second (TPS). Visit the docs for more info.
P50 time to first token (TTFT) on live AI Gateway traffic, in milliseconds. View the docs for more info.
Direct request success rate on AI Gateway and per-provider. Visit the docs for more info.
More models by StepFun
| Model |
|---|
| 256K | 0.7s | 198tps | $0.20/M | $1.15/M | Read:$0.04/M Write:— | — | — |  | 05/28/2026 |