Step 3.5 Flash API

StepFun's Step 3.5 Flash, through an OpenAI-compatible API. Providers quote it on an open exchange, and each request goes to the offer with the lowest estimated charge that meets your rules.

Providers compete for each request. The exchange ranks the offers that meet your rules by estimated charge. It fixes your maximum charge before the first token, and you pay for the tokens that the model uses.
The OpenAI and Anthropic APIs. Use the OpenAI or Anthropic SDK that you have. Set the base URL and your key, and send step-3.5-flash as the model.
Your data rules. Send x-liquid-retention: none and only offers whose provider does not keep your content compete for the request.

Facts

Model name: step-3.5-flash
Maker: StepFun
Context window: 262.1K tokens
Input price: $0.100 per million tokens
Output price: $0.300 per million tokens
Providers: 1 independent provider
Regions: us

Providers

Architect: us, $0.100 input and $0.300 output per million tokens, $0.100 cache read per million tokens, 262.1K tokens of context

Scores

HLE: 24.5, #99 of 273
GPQA: 82.6, #91 of 250
AA-LCR: 63.0, #140 of 237
Terminal-Bench Hard: 32.6, #49 of 166
τ²-Bench: 87.4, #45 of 169
IFBench: 66.5, #55 of 178

Scores: Artificial Analysis (https://artificialanalysis.ai/)

Request

curl https://router.inference.ai.exchange/v1/chat/completions \
  -H "Authorization: Bearer $LIQUID_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "step-3.5-flash",
    "messages": [{"role":"user","content":"Say hello."}]
  }'

Questions

What is Step 3.5 Flash?: Served by intent-router: each job goes to the cheapest healthy upstream for this model.
How much does Step 3.5 Flash cost?: Offers now ask $0.100 per million input tokens and $0.300 per million output tokens. A job pays for the tokens it uses. The exchange picks the cheapest eligible offer.
What is the context length of Step 3.5 Flash?: The largest offer takes 262,144 input tokens. A smaller offer can take less. The exchange skips an offer that cannot take your message.
What can Step 3.5 Flash do?: Its providers list Reasoning effort, JSON object, JSON schema, Frequency penalty, Logit bias, Log probabilities, Min-p sampling, Presence penalty, Repetition penalty, Seed, Stop sequences, Top-k sampling, Top-p sampling, Text, Tools.
What inputs and outputs does Step 3.5 Flash support?: Text → Text.
Which providers serve Step 3.5 Flash?: 1 independent provider quote it now, with 1 offer. The table above ranks them by the cost of a typical job.
How do I call Step 3.5 Flash?: Send "step-3.5-flash" as the model in an OpenAI or Anthropic request. The API section links to setup steps for each client.
When was Step 3.5 Flash listed?: The exchange first listed it on 10/8/2026. This is not its release date.