StepFun (China): Step 3.5 Flash 2603

Quickstart

Use your Moduck API Key, set the API base URL to https://api.moduck.ai/v1, and set the model parameter to stepfun/step-3.5-flash-2603.

import os
import requests

base_url = "https://api.moduck.ai/v1"
api_key = os.environ["MODUCK_API_KEY"]
model_id = "stepfun/step-3.5-flash-2603"

response = requests.post(
    f"{base_url}/chat/completions",
    headers={
        "Authorization": f"Bearer {api_key}",
        "Content-Type": "application/json",
    },
    json={
        "model": model_id,
        "messages": [{"role": "user", "content": "Hello!"}],
        "stream": False,
    },
    timeout=60,
)
response.raise_for_status()
print(response.json())

Use the familiar OpenAI-style chat request format to make model integration easier.

Step 3.5 Flash 2603 API Pricing

Benchmarks

Performance

Measured on the Moduck gateway across live traffic, hour by hour over the last 24 hours. Time to first token is how long before anything appears; throughput is how fast the answer is written after that; end-to-end latency is the whole round trip. Figures are medians unless the card says otherwise.

Artificial Analysis measurement

Availability

Uptime is the share of time at least one provider serving this model responded. Availability is stricter: the share of requests actually served. A provider that answers but fails part of the traffic lowers availability without lowering uptime. Both cover the last three days.

Step 3.5 Flash 2603 Compare models

Model specifications

Input

text

Output

text

Context window

256,000

Maximum input

256,000

Maximum output

256,000

Release date

2026-04-02

Attachments

No

Reasoning

Yes

Tool calling

Yes

Temperature setting

Yes

Open weights

Yes

Frequently asked questions

Related models

No related catalog models are recorded for this model family.