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Create a new session

Create a new session with required title and optional custom system prompt. Session automatically gets isolated storage directory.

Create a new session with required title and optional custom system prompt. Session automatically gets isolated storage directory.

POST
/api/sessions

Request Body

customSystemPrompt?string

Custom system prompt content. Size limits apply based on promptMode: 100KB (102,400 bytes) for replace mode, 50KB (51,200 bytes) for append mode. Ignored in default mode. Supports environment variable substitution with $ syntax.

Lengthlength <= 102400
promptMode?string

Custom prompt handling mode:

  • 'default': Use base system prompt only (customSystemPrompt ignored)
  • 'append': Append customSystemPrompt to base system prompt (50KB limit)
  • 'replace': Replace base system prompt with customSystemPrompt (100KB limit)
Default"default"
Value in"default" | "append" | "replace"
titlestring

Title for the session

Response Body

from mix_python_sdk import Mixwith Mix() as mix:    res = mix.sessions.create(title="<value>", custom_system_prompt="You are a helpful assistant specialized in $<domain>. Always be concise and accurate.", prompt_mode="append")    # Handle response    print(res)
{
  "assistantMessageCount": 0,
  "completionTokens": 0,
  "cost": 0.1,
  "createdAt": "2019-08-24T14:15:22Z",
  "firstUserMessage": "string",
  "id": "string",
  "promptTokens": 0,
  "title": "string",
  "toolCallCount": 0,
  "userMessageCount": 0
}

{
  "error": {
    "code": 400,
    "message": "promptMode must be 'default', 'append', or 'replace'",
    "type": "validation_error"
  }
}