Step-3.5-Flash

apache-2.0

Step 3.5 Flash is an open-source reasoning model by StepFun with 196B total parameters (11B active) using Mixture of Experts. It features a 256K context window, deep reasoning, tool calling, and agentic capabilities, achieving 97.3 on AIME 2025 and 74.4% on SWE-bench Verified.

Context
262K
Input price
$0.09/1M tokens
Output price
$0.3/1M tokens

Capabilities

Reasoning & Interaction
Reasoning
Tool Calling
Output Control
Structured Output
JSON Mode
Infrastructure
Streaming
Fine-tuning

Details

Model IDstepfun-ai/Step-3.5-Flash
Provider DeepInfra
Creator StepFun
Familystep-3
Licenseapache-2.0
Statusactive
Typechat
Input modalitiestext
Output modalitiestext
Open weightYes
Parameters—
Architecture—
Context window262K tokens
Max input—
Max output—
Reasoning tokensYes
Knowledge cutoff—
Release date—
Sourceofficial

Tools

Function Callingfunction_calling
Call external functions and APIs

Endpoints

Chat CompletionsPOST
Generate chat responses with messageshttps://api.deepinfra.com/v1/openai/v1/chat/completions

Pricing

Input
$0.09
Output
$0.3
Cache write
—
Cache read
$0.02
Batch in
—
Batch out
—

API

GET/v1/models/deepinfra/stepfun-ai/Step-3.5-Flash