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Step 3.5 Flash

Tools
stepfun-ai/step-3.5-flash

256K context · Jun 2026 · 7 upstreams

Step 3.5 Flash is a sparse Mixture-of-Experts model by StepFun with 196.81B total parameters (196B backbone + 0.81B MTP head) and ~11B active per token. Built on a 45-layer transformer with 288 routed experts (Top-8 selection), 3:1 SWA attention ratio, and 256K context. Achieves 100–300 tok/s throughput (peaking at 350 tok/s for coding) for frontier reasoning and agentic tasks.

Needs your own keyTo use Step 3.5 Flash, add a key from Nous Research, StepFun, StepFun Step Plan or 4 more. AnyRouter adds no fee.
context
256K
input / 1M (list)
$0.10
output / 1M (list)
$0.30
routes
7
speed, 24h
—

Upstreams

7
  1. 1Nous ResearchYour key · not addedyour planTPS —TTFT ——
  2. 2StepFunYour key · not addedyour planTPS —TTFT ——
  3. 3StepFunYour key · not addedyour planTPS —TTFT ——
  4. 4CommandCodeYour key · not addedyour planTPS —TTFT ——
  5. 5OpenRouterYour key · not addedyour planTPS —TTFT ——
  6. 6SiliconFlowYour key · not addedyour planTPS —TTFT ——
  7. 7Hugging FaceYour key · not addedyour planTPS —TTFT ——
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Try it

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Details

Owner
StepFun AI
Kind
Chat
Released
Jun 2026
Context
256K
Data policy
Provider retention
Endpoint
/api/v1/chat/completions

Quick start

curl https://anyrouter.dev/api/v1/chat/completions \
  -H "Authorization: Bearer $ANYROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "stepfun-ai/step-3.5-flash",
  "messages": [
    {
      "role": "user",
      "content": "Say hi in 3 words."
    }
  ]
}'