StepFun 3.5 Flash

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.

Model overview

Model ID: stepfun/step-3.5-flash
Provider: stepfun
Type: language
Context window: 262,114 tokens
Max output tokens: 262,114

Tags: reasoning, tool-use, implicit-caching

Model pricing

Metric	Value
`Input tokens (/1M)`	`$0.09`
`Output tokens (/1M)`	`$0.30`
`Image generation`	`n/a`
`Cached input read (/1M)`	`n/a`
`Cached input write (/1M)`	`$0.02`
`Pricing source`	`gateway`

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