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StepFun (阶跃星辰)Open-weight·262K context·— params

Step 3.5 Flashstepfun/step-3-5-flash

Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token....

Cheapest blended:$0.15 / 1M tokenson StepFun · 1 provider listed

Pricing across providers

Sort by:
ProviderInput /1MOutput /1MBlended /1MLatency p50FormatFreshnessAction
StepFun
step-3.5-flash
$0.10$0.30$0.15—OpenAI-compatibleNeeds 27d agoTry →

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Works with

Point any of these clients at a hosting's base URL — they all speak at least one of this model's endpoint protocols (OPENAI_COMPATIBLE).

Capabilities

  • chat
  • reasoning
  • code

Languages: zh, en

Code samples

Example using StepFun — the cheapest hosting for this model as of last verification. Swap base_url and model to use a different provider from the matrix above.

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://api.stepfun.com/v1",
)

response = client.chat.completions.create(
    model="step-3.5-flash",
    messages=[{"role": "user", "content": "Hello!"}],
)
print(response.choices[0].message.content)

Technical specs

Context
262K
Max output
66K
Parameters
—
Release
—
Training cutoff
—
License
—
Hugging Face →Official blog →

Similar models

Compare with

  • Step 3.5 Flash vs DeepSeek V3.1
    Comparison planned — not yet published
  • Step 3.5 Flash vs R1
    Comparison planned — not yet published
  • Step 3.5 Flash vs DeepSeek V3
    Comparison planned — not yet published

Frequently asked

How much does Step 3.5 Flash cost?+
The cheapest public hosting is $0.15 per 1M blended tokens on StepFun. 1 total providers are listed above with per-input / per-output / cached pricing.
Is Step 3.5 Flash open-source? Can I fine-tune it?+
Yes. Step 3.5 Flash is open-weight under the unspecified license. Weights are available on Hugging Face for local inference, fine-tuning, and commercial use (see license for specific terms).
Is Step 3.5 Flash OpenAI-compatible?+
Most listed hostings expose an OpenAI-compatible API, so you can point an existing openai SDK client at the Provider's base_url and use the Provider's model name. See the Code Samples above for a copy-pasteable example.
What's the maximum context window for Step 3.5 Flash?+
The model supports up to 262,144 tokens of context (input + output). Some hosted versions may impose a smaller limit — check the "Context" column in the pricing matrix for each provider.