# StepFun: step-3.5-flash-2603 — API on ChinaAPI

> StepFun step-3.5-flash-2603 — the agent-tuned 256K snapshot of step-3.5-flash, optimized for token efficiency and a low-inference operating mode. Its reasoning_effort parameter accepts only low and high, where the base model takes three levels. Text-only, with tool calling, JSON Schema structured output, streaming, and prompt caching.

- Canonical page: https://chinaapi.ai/models/step-3.5-flash-2603/
- Model ID: `step-3.5-flash-2603`
- 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-2603

## 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-2603",
    "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-2603",
    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-2603?**
Use step-3.5-flash-2603 through ChinaAPI with an API key and the OpenAI-compatible endpoint shown on this page.

**How much does step-3.5-flash-2603 cost?**
step-3.5-flash-2603 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-2603 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-2603/ — generated by scripts/gen_model_pages.py. Full catalog: https://chinaapi.ai/llms-full.txt