Step 3.5 Flash is StepFun's open-source reasoning model built on a sparse Mixture of Experts architecture with 196.81B total parameters and roughly 11B active per token. It delivers high throughput through a 45-layer transformer, 3-way multi-token prediction, and hybrid sliding-window attention, generating 100-300 tokens per second in typical usage. The model excels at agentic coding and software engineering, achieving 74.4% on SWE-bench Verified and 97.3 on AIME 2025. It provides reliable function calling and tool orchestration for multi-step task decomposition. Key strengths include a 256K token context window for long-document processing, Apache 2.0 licensing, and open weights for self-hosting. The model targets a strong speed-to-capability ratio, making it well-suited for real-time agent workflows, logical reasoning, mathematics, deep research, and complex task planning.
Step 3.5 Flash runs on 1 route through the Opper gateway. Compare residency, ZDR, and training posture at a glance — full data-handling detail per route below.
| Provider | Region | Zero data retention | Training | Input | Output |
|---|---|---|---|---|---|
| US | Enterprise | No | $0.09 | $0.30 |
Step 3.5 Flash runs on a single route through the Opper gateway today, so its availability is that provider's availability.
Name a second model in the same request and the gateway tries it on retriable errors, so a busy hour never has to reach your users. Set up a fallback chain.
Measured over the last 30 days from each provider's official status feed via StatusGator. Refreshed hourly. See uptime for every provider Opper monitors.
Each route hosting Step 3.5 Flash has its own privacy posture, residency, and GDPR terms. Postures are maintained by Opper with a last-verification timestamp.
Zero data retention is available via Opper Enterprise contract. No training on customer data. US; unknown.
Call Step 3.5 Flash through the Opper gateway with one API key. Let your coding agent set it up, or call it directly — Opper is drop-in compatible with the OpenAI, Anthropic, and Google AI SDKs.
Copy this and paste it into a coding agent like Claude Code, Cursor or Codex and it'll wire up Opper for you.
import OpenAI from "openai";const client = new OpenAI({apiKey: process.env.OPPER_API_KEY,baseURL: "https://api.opper.ai/v3/compat",});const completion = await client.chat.completions.create({model: "deepinfra/stepfun-ai/Step-3.5-Flash",messages: [{ role: "user", content: "Hello" }],});console.log(completion.choices[0].message.content);
Side-by-side on privacy, EU hosting, pricing, and benchmarks.
