MODELS / STEPFUN

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.

TEXTREASONINGREASONINGTOOL-USEIMPLICIT-CACHING
262.1K
CONTEXT WINDOW
262.1K
MAX OUTPUT TOKENS
$0.09 / 1M tokens
INPUT PRICE
$0.3 / 1M tokens
OUTPUT PRICE
QUICKSTART

Call it in one request.

OpenAI-compatible — change the base URL, and the setup is complete.

SHELL
curl https://enterprise.blackbox.ai/v1/chat/completions \
  -H "Authorization: Bearer $BLACKBOX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "blackboxai/stepfun/step-3.5-flash",
    "messages": [{ "role": "user", "content": "Hello!" }],
    "stream": true
  }'
INPUT: textOUTPUT: textRELEASED: 2026-01-29
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STEPFUN

Step 3.7 Flash

256K context · $0.2 / 1M tokens input · $1.15 / 1M tokens output