Optionaladcp_The AdCP major version the buyer's payloads conform to. Sellers validate against their supported major_versions and return VERSION_UNSUPPORTED if unsupported. When omitted, the seller assumes its highest supported version.
Natural language description of user intent — the conversation handoff from the host describing what the user needs from the brand agent
OptionalcontextOptionalmedia_AdCP media buy ID if session was triggered by advertising
OptionalplacementWhere this session was triggered (e.g., 'chatgpt_search', 'claude_chat')
Optionaloffering_Brand-specific offering identifier to apply
Optionalsupported_Optionaloffering_Token from si_get_offering response for session continuity. Brand uses this to recall what products were shown to the user, enabling natural references like 'the second one' or 'that blue shoe'.
Client-generated unique key for this request. Prevents duplicate session creation on retries. MUST be unique per (seller, request) pair to prevent cross-seller correlation. Use a fresh UUID v4 for each request.
Optionalext
Host initiates a session with a brand agent