# StepFun: step-3.5-flash — API on ChinaAPI

> StepFun step-3.5-flash — text-only reasoning model with 256K context for logic, mathematics, software engineering, and deep research. Reasoning depth is selectable per request (low, medium, high), with tool calling, JSON Schema structured output, streaming, and prompt caching.

- Canonical page: https://chinaapi.ai/models/step-3.5-flash/
- Model ID: `step-3.5-flash`
- Context window: 256K
- Modalities: Text
- Pricing: $0.1/M input, $0.3/M output tokens (USD)
- Endpoint: OpenAI-compatible `POST https://api.chinaapi.ai/v1/chat/completions`
- Pricing basis: Token-model rates are synchronized from the gateway and may follow providers' official China list prices where configured. Live pricing is authoritative.
- Access: no mainland-China account or phone number required; $2 free trial credit
- Sign up: https://dash.chinaapi.ai/register?lang=en&utm_source=chinaapi&utm_medium=model-md&utm_campaign=step-3.5-flash

## Quickstart

```
curl -X POST https://api.chinaapi.ai/v1/chat/completions \
  -H "Authorization: Bearer $CHINAAPI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "step-3.5-flash",
    "messages": [
      {"role": "user", "content": "Summarize the main tradeoffs for this API workload."}
    ]
  }'

import os
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["CHINAAPI_API_KEY"],
    base_url="https://api.chinaapi.ai/v1",
)

response = client.chat.completions.create(
    model="step-3.5-flash",
    messages=[
        {"role": "user", "content": "Summarize the main tradeoffs for this API workload."}
    ],
)
print(response.choices[0].message.content)
```

## FAQ

**How do I use step-3.5-flash?**
Use step-3.5-flash through ChinaAPI with an API key and the OpenAI-compatible endpoint shown on this page.

**How much does step-3.5-flash cost?**
step-3.5-flash is $0.1/M input, $0.3/M output tokens, paid in USD. The live pricing page is authoritative. Token-model rates are synchronized from the gateway and may follow providers' official China list prices where configured. Live pricing is authoritative.

**Does step-3.5-flash need a Chinese account?**
No. ChinaAPI provides access without a mainland-China account or phone number and includes a $2 free trial. Check live pricing for the displayed USD rate.

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Markdown twin of https://chinaapi.ai/models/step-3.5-flash/ — generated by scripts/gen_model_pages.py. Full catalog: https://chinaapi.ai/llms-full.txt