Reasoning Model Integration - StepFun Documentation

Step Plan supports accessing StepFun reasoning models via a dedicated path. All requests uniformly use the /step_plan/v1/... path prefix, and the domain name is fixed as https://api.stepfun.ai.

Prerequisites

Subscribed to a Step Plan.
Obtained an API Key.

Supported Models

Model	Description
`step-3.5-flash-2603`	Optimized from Step 3.5 Flash for high-frequency Agent scenarios. Improved token efficiency and faster inference; can switch to low-inference mode to significantly reduce token consumption.
`step-3.5-flash`	Sparse MoE architecture with 196B total / 11B activated parameters. High-speed inference, optimized for agent and coding tasks.

Endpoint Paths

Capability	Request Method	Step Plan Path
Chat Completion (OpenAI protocol)	POST	`https://api.stepfun.ai/step_plan/v1/chat/completions`
Messages (Anthropic protocol)	POST	`https://api.stepfun.ai/step_plan/v1/messages`

The endpoint parameters are exactly the same as the open platform. For details, see the Chat Completion API docs and the Messages API docs.

The Anthropic SDK automatically appends /v1/messages to the base URL, so when using the Anthropic SDK, set the base URL to https://api.stepfun.ai/step_plan (without /v1). The OpenAI SDK uses https://api.stepfun.ai/step_plan/v1.

Billing

The billing logic is consistent with the open platform. The actual amount billed on the open platform is converted into Step Plan total quota consumption. For details on plan entitlements, see the Step Plan overview.

Integration Methods

Direct API Calls

curl
Python (OpenAI SDK)
Python (Anthropic SDK)

curl -X POST 'https://api.stepfun.ai/step_plan/v1/chat/completions' \
-H 'Content-Type: application/json' \
-H "Authorization: Bearer $STEP_API_KEY" \
-d '{
    "model": "step-3.5-flash-2603",
    "messages": [
        {"role": "user", "content": "Hello, please introduce yourself."}
    ]
}'

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_STEP_API_KEY",
    base_url="https://api.stepfun.ai/step_plan/v1",
)

response = client.chat.completions.create(
    model="step-3.5-flash-2603",
    messages=[
        {"role": "user", "content": "Hello, please introduce yourself."}
    ],
)

print(response.choices[0].message.content)

from anthropic import Anthropic

# Note: The Anthropic SDK automatically appends /v1/messages; base_url should not include /v1
client = Anthropic(
    api_key="YOUR_STEP_API_KEY",
    base_url="https://api.stepfun.ai/step_plan",
)

message = client.messages.create(
    model="step-3.5-flash-2603",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Hello, please introduce yourself."}
    ],
)

print(message.content[0].text)

Via Tool Integrations

Reasoning models can be integrated through a variety of Agent tools and coding assistants. Just set the Base URL to https://api.stepfun.ai/step_plan/v1 and select step-3.5-flash-2603 or step-3.5-flash as the model. See the Quick Start and the individual tool integration guides:

OpenClaw

Command-driven Agents and initialization-based workflows.

Claude Code

Coding, debugging, and engineering collaboration in the terminal.

Hermes-Agent

Open-source AI Agent framework for terminals or messaging platforms.

Open Code

Drive development tasks in the terminal with natural language.

Step Plan

Integration Guide

​Prerequisites

​Supported Models

​Endpoint Paths

​Billing

​Integration Methods

​Direct API Calls

​Via Tool Integrations

OpenClaw

Claude Code

Hermes-Agent

Open Code

Prerequisites

Supported Models

Endpoint Paths

Billing

Integration Methods

Direct API Calls

Via Tool Integrations