Step 3.5 Flash
Summary
Step 3.5 Flash is an open-weight language model from StepFun, released on 29 Jan 2026. It accepts text and generates text, with a 262K-token context window and up to 66K output tokens per response. As of 4 Oct 2026, the lowest listed API price is $0.09 per million input tokens and $0.30 per million output tokens (Vercel AI Gateway), across 4 providers we track.
StepFun flash lane for quick multimodal reasoning and coding assistance
Last verified 4 Oct 2026. Every figure on this page links to its source.
Specifications
| Developer | StepFun |
|---|---|
| Release date | 29 Jan 2026 [models.dev] |
| Status | Generally available [models.dev] |
| Weights | Open weights [Hugging Face] |
| License | apache-2.0 [Hugging Face] |
| Parameters | 199B [Hugging Face] |
| Context window | 262K (262,144 tokens) [models.dev] |
| Max output | 66K tokens [models.dev] |
| Knowledge cutoff | Jan 2025 [models.dev] |
| Input | Text [models.dev] |
| Output | Text [models.dev] |
| Reasoning mode | Yes [models.dev] |
| Tool calling | Yes [models.dev] |
| Structured output | No [models.dev] |
| Hugging Face | stepfun-ai/Step-3.5-Flash [Hugging Face] |
Step 3.5 Flash API pricing by provider
USD per million tokens. Sorted by input price.
| Provider | Input | Output | Cached input | Context | Source |
|---|---|---|---|---|---|
| Vercel AI Gateway stepfun/step-3.5-flash | $0.09 | $0.30 | $0.02 | 262K | models.dev, 4 Oct 2026 |
| SiliconFlow stepfun-ai/Step-3.5-Flash | $0.10 | $0.30 | – | 262K | models.dev, 4 Oct 2026 |
| Hugging Face Inference Providers stepfun-ai/Step-3.5-Flash | $0.10 | $0.30 | – | 262K | models.dev, 4 Oct 2026 |
| OpenRouter stepfun/step-3.5-flash | $0.10 | $0.30 | – | 262K | OpenRouter, 4 Oct 2026 |
Frequently asked questions
What is the context window of Step 3.5 Flash?
Step 3.5 Flash has a context window of 262,144 tokens (262K) and can generate up to 65,536 tokens in a single response, according to models.dev.
How much does the Step 3.5 Flash API cost?
Step 3.5 Flash is listed from $0.09 per million input tokens and $0.30 per million output tokens (Vercel AI Gateway). Prices last verified 4 Oct 2026.
Is Step 3.5 Flash open source?
Step 3.5 Flash is an open-weight model: its weights are published on Hugging Face as stepfun-ai/Step-3.5-Flash under the apache-2.0 license. Check the license terms before commercial use.
When was Step 3.5 Flash released?
StepFun released Step 3.5 Flash on 29 Jan 2026, according to models.dev.
Which providers offer Step 3.5 Flash?
We track Step 3.5 Flash on 4 providers: Vercel AI Gateway, SiliconFlow, Hugging Face Inference Providers, OpenRouter.
Change history
No changes detected since we started tracking this model. We re-check every source daily.
Sources
- https://openrouter.ai/stepfun/step-3.5-flash
- https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/stepfun/step-3.5-flash.toml
- https://huggingface.co/stepfun-ai/Step-3.5-Flash
- https://github.com/sst/models.dev/blob/dev/providers/vercel/models/stepfun/step-3.5-flash.toml
- https://github.com/sst/models.dev/blob/dev/providers/siliconflow/models/stepfun-ai/Step-3.5-Flash.toml
- https://github.com/sst/models.dev/blob/dev/providers/huggingface/models/stepfun-ai/Step-3.5-Flash.toml