Step 3.5 Flash pricing, context and benchmark
Step 3.5 Flash is StepFun's most capable open-source foundation model.
Everything that matters, in one table
Context, pricing, cache, modalities and tooling, from the model registry and Artificial Analysis.
| Model | Step 3.5 Flash |
| Model ID | stepfun/step-3.5-flash |
| Provider | Stepfun |
| Release date | 29 January 2026 |
| Status | Generally available |
| Input context | 262,144 tokens |
| Output context | 65,536 tokens |
| Official input pricing | $0.1 per 1M tokens |
| Official output pricing | $0.3 per 1M tokens |
| Cache read pricing | $0.02 per 1M tokens (80% off input) |
| Market input pricing | $0.1 per 1M (cheapest route) |
| Market output pricing | $0.3 per 1M (cheapest route) |
| Input modalities | text |
| Output modalities | text |
| Reasoning control | Not exposed |
| Tool support | Text generation only |
| Tokenizer | Other |
| Provider routes | 1 endpoint |
| Artificial Analysis index | Not published |
| Speed | 101 tokens/s, 25.3s to first token |
| Knowledge cutoff | Not publicly stated |
Input and output support
| Modality | Input | Output | Billed at |
|---|---|---|---|
| Text | ✓ yes | ✓ yes | $0.1 in |
| Image | no | no | not supported |
| Audio | no | no | not supported |
| Video | no | no | not supported |
| File (PDF) | no | no | not supported |
What is Step 3.5 Flash?
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....
Step 3.5 Flash carries a 262K token window, uses the Other tokenizer and is served by Stepfun. On Hoodgen it sits in the Fast tier of the model menu next to its siblings, so you can switch mid conversation without losing the thread.
Release and what changed from the previous version
This is the only release of Step 3.5 Flash on OpenRouter, released 29 January 2026. The provider has not published a knowledge cutoff, so treat training data as recent but unconfirmed for very new events.
Features and capabilities
What can you do with Step 3.5 Flash?
Prompt caching and how to cut the bill
Cached input bills at $0.02 per million instead of $0.1, a 80% discount. Keep the system prompt and documents first and the changing question last, so every call hits the cache.
Step 3.5 Flash pricing
Official pricing
- $0.02 cached input
- 262K context
- text input
- 1 route on OpenRouter
- What Hoodgen routes to first
- Same model, lower bill
Market pricing, every route
| Provider | Tier | Input | Output | Cache read | Uptime 24h |
|---|---|---|---|---|---|
| SiliconFlow | standard | $0.1 | $0.3 | n/a | 97.3% |
API pricing and cost calculator
| Rate | Per call | Total | Credits |
|---|---|---|---|
| Cheapest route | $0.0024 | $1.22 | 1164 |
| List price | $0.0015 | $0.74 | 708 |
API and developer information
| Model ID | stepfun/step-3.5-flash |
| Endpoint | https://openrouter.ai/api/v1/chat/completions |
| Parameters | prompt and max_tokens |
| Streaming | Yes, server sent events |
| Modality string | text->text |
| Max prompt tokens | 262,144 |
| Max completion tokens | 65,536 |
curl https://openrouter.ai/api/v1/chat/completions \
-H "Authorization: Bearer $OPENROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "stepfun/step-3.5-flash",
"messages": [{ "role": "user", "content": "Summarise this document." }],
"max_tokens": 1024
}'Model limitations
| Text only output | It cannot generate images, audio or video. Pair it with an image model on Hoodgen when you need visuals. |
| Output cap | 65,536 tokens per request. Long deliverables have to be chunked. |
| Benchmarks not published | Artificial Analysis does not publish an Intelligence Index for this release, so no benchmark score is claimed here. |
| Knowledge cutoff | The provider does not state a fixed cutoff for every release. Verify very recent events against search. |
| Depth ceiling | Fast tier: strong on throughput, weaker than flagship tiers on long multi step reasoning. |
Step 3.5 Flash vs other Stepfun models
| Model | Context | Input /1M | Output /1M | AA index | Released |
|---|---|---|---|---|---|
| Step 3.5 Flash | 262K | $0.1 | $0.3 | n/a | 2026 |
| Step 5 Preview | 1M | $1 | $2.7 | n/a | Oct 2026 |
| Step 3.7 Flash | 262K | $0.2 | $1.15 | n/a | 2026 |
Privacy and data policy
- On Hoodgen, prompts and attachments answer that request and stay in your conversation history so you can reopen it. They are not used to train models.
- Requests route through OpenRouter to Stepfun and are covered by that provider's API terms.
- Do not paste secrets or personal data you would not send to any hosted model.
Step 3.5 Flash questions, answered
Start chatting with Step 3.5 Flash
Free to try on Hoodgen AI, with a live credit estimate before every send. No API key, no setup.