Step 3.5 Flash
Built by StepFun, Step 3.5 Flash is an chat model with a 262K token context window. 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 · 262K token context window
Best for
- low-latency chat and routing
- request routing and triage
- text classification
Ways to use Step 3.5 Flash in osFoundry
Connect with your own key (BYOK)
Open the key dialog and paste your StepFun API key. osFoundry discovers Step 3.5 Flash automatically — assign it to a Maestro role (router, direct, orchestrator, or fallback) in the Pipeline tab and it is live in every chat. Your key, your provider account — no token markup.
Use it in a Room App
Room Apps declare AI features in their manifest, then call them with invokeAI:
import { invokeAI } from '@osfoundry/app-sdk'
// 'summarize' is an AI feature declared in your app manifest.
const result = await invokeAI('summarize', userText)
Call it from your own apps
Once a model is wired into your workspace you can host it as an API and reach it from your own services, scripts, or CI — outside osFoundry.
Run Step 3.5 Flash yourself
Step 3.5 Flash is also available as open weights — self-host it for full data control and no per-token cost. See that page for GPU requirements and a cost comparison against API pricing.
Step 3.5 Flash vs similar models
Licence
Hosted — usage subject to provider terms — Hosted-only model — usage governed by the provider's API terms. Bring your own provider key.
No weights distributed; usage subject to provider terms.
Frequently asked about Step 3.5 Flash
How much does Step 3.5 Flash cost?
Step 3.5 Flash is metered at $ 0.100 /1M for input, and $ 0.300 /1M for output. Bring your own StepFun API key — osFoundry passes through provider pricing without markup.
Can I use Step 3.5 Flash commercially?
Commercial use is allowed with conditions. Hosted-only model — usage governed by the provider's API terms. Bring your own provider key. No weights distributed; usage subject to provider terms.
What is the context window of Step 3.5 Flash?
Step 3.5 Flash supports a 262K token context window.
Can I run Step 3.5 Flash locally?
No — Step 3.5 Flash is hosted only and accessed via the StepFun API. An open-weights equivalent is available to self-host — see the cross-link above.
What is Step 3.5 Flash best at?
Step 3.5 Flash is well-suited to low-latency chat and routing, request routing and triage, text classification.
How do I use Step 3.5 Flash in osFoundry?
Paste your StepFun API key in the key dialog (or deploy the open weights for self-hostable models), assign Step 3.5 Flash to a Maestro role in the Pipeline tab, then use it in chat, Room Apps via invokeAI, or your own apps.
Published by StepFun on January 29, 2026. Source: https://openrouter.ai/stepfun/step-3.5-flash