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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.

ReasoningTool UseImplicit Caching
index.ts
import { streamText } from 'ai'


const result = streamText({
  model: 'stepfun/step-3.5-flash',
  prompt: 'Why is the sky blue?'
})
OverviewPlaygroundProvidersThroughputLatencyUptimeStatusSimilar

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Provider
Context
Latency
Throughput
Input
Output
Cache
Web Search
Per Query
Capabilities
ZDR
No Training
Release Date
DeepInfra
Legal:Terms
•
Privacy
262K
0.2s
49tps
$0.09/M$0.30/M
Read:—
Write:$0.02/M
——
01/29/2026