Step 3.5 Flash

Not rated yet. Independent test results usually appear a few weeks after a model is released.

Benchmark data: Epoch AI, licensed CC BY 4.0

Companies that serve this model through an API: 1. Prices per million tokens, cheapest first.

Availability and prices come from OpenRouter’s public API and are refreshed daily. Uptime is the share of successful requests over the last 24 hours. Some providers run a compressed version of open models (fp8, int4), which is cheaper but can be slightly less accurate.

Call Step 3.5 Flash through OpenRouter’s OpenAI-compatible API: create a key on openrouter.ai, then run one of these examples.

curl https://openrouter.ai/api/v1/chat/completions \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "stepfun/step-3.5-flash", "messages": [{"role": "user", "content": "Hello! What can you do?"}]}'

import os
from openai import OpenAI

client = OpenAI(base_url="https://openrouter.ai/api/v1", api_key=os.environ["OPENROUTER_API_KEY"])
reply = client.chat.completions.create(
    model="stepfun/step-3.5-flash",
    messages=[{"role": "user", "content": "Hello! What can you do?"}],
)
print(reply.choices[0].message.content)

import OpenAI from "openai";

const client = new OpenAI({ baseURL: "https://openrouter.ai/api/v1", apiKey: process.env.OPENROUTER_API_KEY });
const reply = await client.chat.completions.create({
  model: "stepfun/step-3.5-flash",
  messages: [{ role: "user", content: "Hello! What can you do?" }],
});
console.log(reply.choices[0].message.content);

The same code works with every model on this site: only the model ID changes. Many labs also offer their own API and SDK.

• 1,000 chat replies

  ≈ 500 tokens in, 300 out each
  $0.14
• Summarise a 100-page document

  ≈ 50,000 tokens in, 1,000 out
  $0.0053
• An app with 10,000 requests a day for a month

  ≈ 1,000 tokens in, 400 out each
  $66.00

Cost calculator →

How much does Step 3.5 Flash cost?

Step 3.5 Flash costs $0.10 per million input tokens and $0.30 per million output tokens through the API. For example, 1,000 chat replies of about 500 tokens in and 300 out cost around $0.14.

What is the context window of Step 3.5 Flash?

Step 3.5 Flash can read up to 262,144 tokens in one request, about 492 pages of text. It can write up to 65,536 tokens in a single answer.

Is Step 3.5 Flash open source?

Yes. Its weights are published (stepfun-ai/Step-3.5-Flash), so you can download it and run it on your own hardware, or use it through one of 1 API providers.

Who makes Step 3.5 Flash?

Step 3.5 Flash is made by StepFun. It became available through the API on January 29, 2026.

Can Step 3.5 Flash read images?

No. Step 3.5 Flash only accepts text as input.

What are the alternatives to Step 3.5 Flash?

Models with a similar price from other companies include GPT-6 Luna Pro, Muse Spark 1.3 Contributor and Reka Edge. You can compare them side by side on this page.