Inception: Mercury 2.5 Preview

inception/mercury-2.5-preview

Mercury 2.5 is the fastest reasoning LLM, and the latest diffusion LLM (dLLM) from Inception. Instead of generating tokens sequentially, Mercury 2.5 produces and refines multiple tokens in parallel, a...

tools

MODALITIES

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INPUT PRICE

$0.04per 1M

OUTPUT PRICE

$0.15per 1M

CONTEXT

260K

RELEASED

Sep 1, 2026

Provider				Cache	Uptime	Chat
FastAPI	—	$0.04	$0.15	Cache read$0.004

Capabilities

Input modalities

text

Output modalities

text

Features

include_reasoningmax_tokensreasoningreasoning_effortresponse_formatstopstructured_outputstemperaturetool_choicetools

Get API Key

Create an API key from the Keys page, then set it as an environment variable:

export ONLIST_API_KEY=sk-...

Make your first request

Endpoints

POSThttps://onlist.io/v1/chat/completions

OpenAI Chat Completions format

Request Headers

Authorization:Bearer $ONLIST_API_KEY

Content-Type:application/json

Model:inception/mercury-2.5-preview

POSThttps://onlist.io/v1/responses

OpenAI Responses format

Request Headers

Authorization:Bearer $ONLIST_API_KEY

Content-Type:application/json

Model:inception/mercury-2.5-preview

POSThttps://onlist.io/v1/messages

Anthropic Messages format

Request Headers

Authorization:Bearer $ONLIST_API_KEY

Content-Type:application/json

Model:inception/mercury-2.5-preview

Code samples

curl https://onlist.io/v1/chat/completions \
  -H "Authorization: Bearer $ONLIST_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
       "model": "inception/mercury-2.5-preview",
       "messages": [
         {
           "role": "user",
           "content": "Explain quantum entanglement in one paragraph."
         }
       ]
     }'

Replace $ONLIST_API_KEY with the API key from your Keys page.

Authentication

All requests must include an Authorization: Bearer <TOKEN> header. Generate keys from the Keys page; keys can be scoped to specific models, groups, IP ranges, and rate limits.

Enable streaming

Add "stream": true to receive partial responses as server-sent events in real time.

Streaming example

curl https://onlist.io/v1/chat/completions \
  -H "Authorization: Bearer $ONLIST_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
       "model": "inception/mercury-2.5-preview",
       "messages": [
         {
           "role": "user",
           "content": "Write a haiku about recursion."
         }
       ],
       "stream": true
     }'

Supported parameters

Name	Type	Description
`include_reasoning`
`max_tokens`	integer	Maximum number of tokens to generate in the completion.
`reasoning`
`reasoning_effort`	string	Constrains effort on reasoning. Supported values: "low", "medium", "high".
`response_format`	object	Specifies the output format. Use {"type": "json_object"} for JSON mode.
`stop`	string \| array	Up to 4 sequences where the API will stop generating tokens.
`structured_outputs`
`temperature`	number	Sampling temperature between 0 and 2. Higher values make output more random.
`tool_choice`	string \| object	Controls which tool is called. "auto", "none", "required", or a specific function.
`tools`	array	A list of tools the model may call. Currently supports functions.

These are the request parameters this model accepts. Parameter semantics follow the OpenAI Chat Completions specification.