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StepFun: Step 3.5 Flash

Source description (English)

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....

View source on OpenRouter Hugging Face
Overview

Model specifications

Context
262,144 tokens
Maximum output
65,536 tokens
Architecture
text->text
Tokenizer
Other
Knowledge cutoff
Not provided
Moderated
No
OPENROUTER

Complete pricing

Synchronized OpenRouter rates. Token prices are shown per one million tokens.

Input
$0.1
per 1M tokens
Output
$0.3
per 1M tokens
API

Model configuration

Reasoning

Reasoning required
Yes
Default parameters
No
API

Quick start

Set OPENROUTER_API_KEY locally. Python requires requests; JavaScript runs in Node.js. Keep the key on the server.

API documentation

curl --fail-with-body 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!"}]}'
Capabilities

Input → Output

Input
text
Output
text
Reasoning

No

API

Supported API parameters

frequency_penaltyinclude_reasoningmax_tokensreasoningtemperaturetool_choicetoolstop_ktop_p
Available providers

1 Provider

Checked: September 7, 2026

Live providers on OpenRouter

Provider availability, latency, throughput and routing can change continuously. Open the source page for current operational data.

OpenRouter

SiliconFlow

fp8
Context
262K
Maximum output
66K
Input
$0.1
Output
$0.3
Cache read
Not provided
Cache write
Not provided
stepfun

1 models

All models
stepfun logostepfun

StepFun: Step 3.7 Flash

Step 3.7 Flash is StepFun's latest high-efficiency multimodal Mixture-of-Experts model. It pairs a 196B-parameter language backbone with a vision encoder for native image and video understanding, activating roughly 11B parameters...

Context
262K
Input
text · image · video
Output
text
Input: $0.2Output: $1.15per 1M tokens
View model details →