Step 3.5 Flash 2603 | EmpirioLabs AI Docs

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	Yes
Supported endpoints	`POST /v1/chat/completions`, `POST /v1/responses`, `POST /v1/messages`, `POST /v1beta/models/step-3-5-flash-2603:generateContent`

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

$ 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.

Notes

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

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