> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.empiriolabs.ai/models/step-3-5-flash-2603/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.empiriolabs.ai/_mcp/server.

# Step 3.5 Flash 2603

> Agent-optimized Step 3.5 Flash variant with low and high reasoning effort modes.

![Step 3.5 Flash 2603](https://media.empiriolabs.ai/model-logos/step-3-5-flash-2603.png)

[StepFun](/providers/stepfun) · Text Generation

`POST /v1/chat/completions`

Agent-optimized Step 3.5 Flash variant with low and high reasoning effort modes.

## At a glance

| Field               | Value                                                                                                                             |
| ------------------- | --------------------------------------------------------------------------------------------------------------------------------- |
| Model id            | `step-3-5-flash-2603`                                                                                                             |
| Model release date  | 2026-04-02                                                                                                                        |
| Input modalities    | Text                                                                                                                              |
| Output modalities   | Text                                                                                                                              |
| Context window      | 256K                                                                                                                              |
| Weight precision    | -                                                                                                                                 |
| Max output tokens   | 131,072                                                                                                                           |
| Region              | International                                                                                                                     |
| Features            | reasoning, function\_calling, prompt\_cache, agentic\_coding, web\_search                                                         |
| Native inference    | No                                                                                                                                |
| New                 | No                                                                                                                                |
| Structured output   | Not supported                                                                                                                     |
| Supported endpoints | `POST /v1/chat/completions`, `POST /v1/responses`, `POST /v1/messages`, `POST /v1beta/models/step-3-5-flash-2603:generateContent` |
| Alternate model ids | `step-3.5-flash-2603`, `stepfun/step-3-5-flash-2603`, `stepfun/step-3.5-flash-2603`                                               |

## Pricing

| Charge              | Spec                       | Rate    |
| ------------------- | -------------------------- | ------- |
| Input               | per 1M prompt tokens       | \$0.10  |
| Output              | per 1M generated tokens    | \$0.30  |
| Implicit cache read | per 1M cached input tokens | \$0.02  |
| Web Search (Linkup) | per call when invoked      | \$0.013 |

## Example request

```bash
curl https://api.empiriolabs.ai/v1/chat/completions \
  -H 'Authorization: Bearer $EMPIRIOLABS_API_KEY' \
  -H 'Content-Type: application/json' \
  -d '{"model": "step-3-5-flash-2603", "messages": [{"role":"user","content":"Hello"}]}'
```

## Parameters

| Parameter            | Type    | Required | Default     | Description                                                                                                                                                                                                                                                                         |
| -------------------- | ------- | -------- | ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `temperature`        | number  | no       | `0.5`       | Sampling temperature. · Range: 0 – 2                                                                                                                                                                                                                                                |
| `top_p`              | number  | no       | `0.9`       | Nucleus sampling probability mass. · Range: 0 – 1                                                                                                                                                                                                                                   |
| `max_tokens`         | integer | no       | `4096`      | Maximum output tokens. Reasoning tokens count toward this limit. · Range: 1 – 131072                                                                                                                                                                                                |
| `stop`               | array   | no       | -           | Stop sequences.                                                                                                                                                                                                                                                                     |
| `frequency_penalty`  | number  | no       | `0`         | Penalty for repeated tokens. · Range: 0 – 1                                                                                                                                                                                                                                         |
| `reasoning_effort`   | enum    | no       | `"low"`     | Reasoning effort for the agent-optimized Step 3.5 Flash 2603 route. · Allowed: `low`, `high`                                                                                                                                                                                        |
| `reasoning_format`   | enum    | no       | `"general"` | Reasoning trace format returned by StepFun. · Allowed: `general`, `deepseek-style`                                                                                                                                                                                                  |
| `tools`              | array   | no       | -           | OpenAI-compatible function tools.                                                                                                                                                                                                                                                   |
| `tool_choice`        | string  | no       | -           | OpenAI-compatible tool choice.                                                                                                                                                                                                                                                      |
| `web_search_linkup`  | boolean | no       | false       | Optional web search powered by Linkup. When enabled, recent web sources are retrieved using your latest user message as the query and provided to the model as additional context. Adds \$0.013 per call when invoked on top of the model's normal token cost. Disabled by default. |
| `disable_formatting` | boolean | no       | false       | When enabled, the gateway will not append the "Sources" footer to assistant responses that used Linkup web search. Useful when the model output is piped to another system that expects no decoration.                                                                              |

## Notes

Text-only agent model with 256K context, function tools, prompt-cache billing, reasoning\_effort low or high, and optional Linkup web search.

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*Machine-readable schema:* `GET https://api.empiriolabs.ai/v1/models/step-3-5-flash-2603`.

> Agent-optimized Step 3.5 Flash variant with low and high reasoning effort modes.