Step 5 Preview | EmpirioLabs AI Docs

StepFun · Text Generation

POST /v1/chat/completions

Frontier multimodal reasoning with a 1M token context, image and video input, parallel tool calling, and strict JSON schema output.

At a glance

Field	Value
Model id	`step-5-preview`
Model release date	2026-09-15
Input modalities	Text, Image, Video
Output modalities	Text
Context window	1.02M
Weight precision	-
Max output tokens	131,072
Region	International
Features	reasoning, function_calling, structured_output, vision, video, prompt_cache, agentic_coding
Native inference	No
New	Yes
Structured output	JSON Schema
Supported endpoints	`POST /v1/chat/completions`, `POST /v1/responses`, `POST /v1/messages`, `POST /v1beta/models/step-5-preview:generateContent`
Alternate model ids	`stepfun/step-5-preview`

Pricing

Charge	Spec	Rate
Input	per 1M prompt tokens	$1.00
Output	per 1M generated tokens	$2.70
Implicit cache read	per 1M cached input tokens	$0.05
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-5-preview", "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: 0.01 – 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: -2 – 2
`reasoning_effort`	enum	no	`"low"`	Controls how much the model reasons before it answers. Higher effort spends more tokens on reasoning. · Allowed: `low`, `medium`, `high`
`reasoning_format`	enum	no	`"general"`	Format of the reasoning trace returned alongside the answer. · Allowed: `general`, `deepseek-style`
`tools`	array	no	-	OpenAI-compatible function tools.
`tool_choice`	string	no	-	OpenAI-compatible tool choice.
`response_format`	object	no	-	Constrain the output to valid JSON. Use JSON mode for any JSON object, or supply a JSON Schema to force an exact response shape.
`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	Return the answer without the Sources list that web search adds.

Notes

Supports text, image, and video input with a 1M token context, parallel function tools, strict JSON schema output, and reasoning_effort low, medium, or high. Prompt-cache hits are billed at the cache-read rate. Video input supports MP4 under 128 MB, with clips under 5 minutes recommended. This is a preview release, so its behavior and identifier may change.

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