Step 3.5 Flash

Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token....

by StepFun

Overview

Quick stats across all benchmark runs.

Score

31%

5 benchmarks

Avg Latency

23.2s

23 requests

Pricing

$0.09 in / $0.30 out

per 1M tokens

Context

262K

tokens

Alternatives

Models with similar or better quality but different tradeoffs

Same Quality, Cheaper

Models with similar or better performance at a lower cost per token.

No alternatives found

Same Quality, Faster

Models with similar or better performance but lower latency.

Model	Latency
Nova Premier 1.0	-63%

Same Cost, Better

Models at a similar price point with higher benchmark scores.

No alternatives found

Benchmark Performance

How this model performs across different benchmarks

Benchmark	Score	Rank
Explain Like I'm 5	70%	23 / 47
Bad Idea Bench	63%	18 / 23
Product Recommendation Bench	63%	11 / 30
Categorization Bench	37%	35 / 52
Money Boy Cultural Literacy Test	27%	77 / 99

Price vs Performance

Compare cost efficiency across all models

Current model (baseline)

Other models (relative score)

Y-axis shows score difference from shared benchmarks. X-axis uses log scale.

Score Over Time

Performance trends across all benchmark runs

Benchmark Activity

Number of benchmark runs over time

Quickstart

View on OpenRouter

Get started with this model using OpenRouter

import { OpenRouter } from "@openrouter/sdk";

const openrouter = new OpenRouter({
  apiKey: "<OPENROUTER_API_KEY>"
});

const completion = await openrouter.chat.completions.create({
  model: "stepfun/step-3.5-flash",
  messages: [
    {
      role: "user",
      content: "Hello!"
    }
  ]
});

console.log(completion.choices[0].message.content);

Get your API key at openrouter.ai/keys

Other Models from StepFun

Compare performance with other models from the same creator

Model	Latency	Cost/1M	Score
Step 3.7 Flash	3.4s	$0.68	—