How much does Step 3.5 Flash cost?

Step 3.5 Flash is billed pay-as-you-go at $0.13 per 1M input tokens and $0.39 per 1M output tokens. There is no subscription — you only pay for what you use.

What is the context window of Step 3.5 Flash?

Step 3.5 Flash supports a context window of up to 128K tokens. It can return up to 8K tokens in a single response.

What can Step 3.5 Flash do?

Step 3.5 Flash is Stepfun's chat model, accessible through the Api.Airforce API.

Is Step 3.5 Flash free to use?

Step 3.5 Flash is a paid, pay-as-you-go model — no subscription, you are only charged for usage.

How do I use Step 3.5 Flash via the API?

Step 3.5 Flash is OpenAI-compatible. Point any OpenAI SDK at https://api.airforce/v1 and pass the model ID step-3.5-flash with your Api.Airforce API key.

Who makes Step 3.5 Flash?

Step 3.5 Flash is Stepfun's chat model, served through the unified Api.Airforce gateway alongside 100+ other models.

StepfunPaidOperational

Step 3.5 Flash

API model name: step-3.5-flash

Step 3.5 Flash is Stepfun's chat model, served on the Api.Airforce unified API. It has a 128K-token context window. It is priced at $0.13 per million input tokens and $0.39 per million output tokens. Knowledge cutoff: 2025-05. Access it through the OpenAI-compatible API with one key, alongside 100+ other models on Api.Airforce.

Get an API key View pricing

Pricing

Input / 1M tokens

$0.13

Output / 1M tokens

$0.39

Cache read / 1M tokens

$0.01

Specifications

Provider: Stepfun
Type: chat model
Context window: 128K tokens
Max output: 8K tokens
Knowledge cutoff: 2025-05
Input: text
Output: text

Capabilities

Streaming

What is Step 3.5 Flash used for?

Chatbots & assistants — conversational AI, drafting, summarizing and Q&A.
Real-time experiences — stream tokens for responsive chat and apps.

Step 3.5 Flash vs. similar models

Model	Intelligence	Context	Input / 1M	Output / 1M
Step 3.5 Flash	—	128K	$0.13	$0.39
GPT 5.5 High	—	—	$0.96	$5.75
GPT 5.5 High Openai Compact	—	—	$0.77	$4.63
GPT 5.5 Low	—	—	$0.96	$5.75

Prices are Api.Airforce pay-as-you-go rates per 1M tokens. Context is the maximum input length.

Step 3.5 Flash — frequently asked questions

How much does Step 3.5 Flash cost?: Step 3.5 Flash is billed pay-as-you-go at $0.13 per 1M input tokens and $0.39 per 1M output tokens. There is no subscription — you only pay for what you use.
What is the context window of Step 3.5 Flash?: Step 3.5 Flash supports a context window of up to 128K tokens. It can return up to 8K tokens in a single response.
What can Step 3.5 Flash do?: Step 3.5 Flash is Stepfun's chat model, accessible through the Api.Airforce API.
Is Step 3.5 Flash free to use?: Step 3.5 Flash is a paid, pay-as-you-go model — no subscription, you are only charged for usage.
How do I use Step 3.5 Flash via the API?: Step 3.5 Flash is OpenAI-compatible. Point any OpenAI SDK at https://api.airforce/v1 and pass the model ID step-3.5-flash with your Api.Airforce API key.
Who makes Step 3.5 Flash?: Step 3.5 Flash is Stepfun's chat model, served through the unified Api.Airforce gateway alongside 100+ other models.

All models·Quickstart·Chat API reference

Use Step 3.5 Flash via the API

OpenAI-compatible — point any OpenAI SDK at https://api.airforce/v1 and pass step-3.5-flash as the model.

cURL

curl https://api.airforce/v1/chat/completions \
  -H "Authorization: Bearer $AIRFORCE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "step-3.5-flash",
    "messages": [{ "role": "user", "content": "Hello!" }]
  }'

Python

from openai import OpenAI
client = OpenAI(base_url="https://api.airforce/v1", api_key="$AIRFORCE_API_KEY")
r = client.chat.completions.create(
    model="step-3.5-flash",
    messages=[{"role": "user", "content": "Hello!"}],
)
print(r.choices[0].message.content)

JavaScript

import OpenAI from "openai";
const client = new OpenAI({ baseURL: "https://api.airforce/v1", apiKey: process.env.AIRFORCE_API_KEY });
const r = await client.chat.completions.create({
  model: "step-3.5-flash",
  messages: [{ role: "user", content: "Hello!" }],
});
console.log(r.choices[0].message.content);