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 11
No signup required — 10,000 session credits for guests. 50,000 free credits on account creation.
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....
Very large context window — 262,144 tokens (paste entire codebases or long PDFs).
Extremely low per-token price compared to frontier models — good for high-volume workloads.
Hosted by Stepfun — you can access it here alongside GPT-4o, Claude, Gemini and 100+ more on one plan.
Switch to any other model mid-conversation from the picker.
Around 209–524 credits per typical message. 15M Pro credits buy roughly 28,625–71,770 messages.
StepFun: Step 3.5 Flash is a chat/completion model served by Stepfun and accessed through Faceb.ai. Try it without signing up — guest users get 10,000 session credits to experiment.
You get 50,000 credits on signup — usually enough for a handful of messages. After that, Pro is $14.99/month for 15M credits, or top-ups from $5.
262,144 tokens. Paste your source material in, no need to truncate.
Yes. Any API key from /account/api/ works with model slug `stepfun/step-3.5-flash`. The OpenAI SDK works with base_url=https://api.faceb.ai/v1.
Depends on the task. Faceb.ai lets you switch models per message — benchmark side-by-side by asking both the same prompt, which is more reliable than abstract comparisons.
Around 209–524 credits per typical message. 15M Pro credits buy roughly 28,625–71,770 messages.
No. We contractually request that upstream providers not train on content routed through us. Your chat history lives only on your account.
It depends on the model size and training mix. For serious code work the developer favourites are Claude 3.5 Sonnet and DeepSeek V3; for quick edits, most capable models work fine.
Yes — point your SDK at https://api.faceb.ai/v1 and use this model's slug as the model parameter. Everything else works as normal.
Check the model catalog — multimodal models are marked in the picker. If it accepts images, you can drop screenshots and diagrams straight into the chat.
Yes — the picker is always at the top of the chat. Previous context carries over.
Yes. Our catalog auto-fetches from the upstream aggregator, so provider updates and new versions appear in the picker as soon as they're available.
Your Faceb.ai credits work for every model — switch per message, no extra subscriptions.
OpenAI's flagship multimodal model — text, vision, and code.
Chat with GPT-4o →OpenAI's fastest, cheapest frontier model — great default.
Chat with GPT-4o mini →Anthropic's best balance of quality and cost — a coder favourite.
Chat with Claude 3.5 Sonnet →One subscription covers every frontier model — switch between them per message. No extra API keys, no extra bills.
Start chatting with StepFun: Step 3.5 Flash → Go Pro · $14.99/mo