si_terminate_session

si_terminate_session is the AdCP task for ending an SI session. Supports five termination reasons including transaction handoff to ACP, with follow-up suggestions and checkout context for commerce.

Experimental. Sponsored Intelligence (si_get_offering, si_initiate_session, si_send_message, si_terminate_session) is part of AdCP 3.0 as an experimental surface — it may change between 3.x releases with at least 6 weeks’ notice. Sellers implementing any of these tasks MUST declare sponsored_intelligence.core in experimental_features. See experimental status for the full contract.

End an SI session. Either the host or brand agent can initiate termination, with different reasons indicating how the session concluded.

Request

Field	Type	Required	Description
session_id	string	Yes	Session ID to terminate
reason	string	Yes	Why the session is ending
termination_context	object	No	Additional context for the termination

Termination Reasons

Reason	Meaning	Typical Initiator
handoff_transaction	User wants to complete a purchase	Brand agent (via pending_handoff)
handoff_complete	Conversation naturally concluded	Brand agent
user_exit	User explicitly ended the conversation	Host
session_timeout	Inactivity timeout reached	Host
host_terminated	Host ended for policy/error reasons	Host

Termination Context Object

Additional details vary by reason:

For handoff_transaction:

{
  "intent": { /* purchase intent from handoff */ },
  "context_for_checkout": { /* ACP context */ }
}

For user_exit:

{
  "user_signal": "changed_topic",
  "partial_context": { /* what was discussed */ }
}

For session_timeout:

{
  "last_activity": "2026-01-18T10:30:00Z",
  "timeout_seconds": 300
}

Response

Field	Type	Description
session_id	string	Confirms which session was terminated
terminated	boolean	Always true on success
acp_handoff	object	Present for transaction handoffs
follow_up	object	Optional actions for future engagement

ACP Handoff Object

For transaction terminations, includes data needed for ACP checkout:

Field	Type	Description
checkout_url	uri	Brand’s ACP checkout endpoint. Hosts MUST validate this is HTTPS.
checkout_token	string	Opaque token to pass to the checkout endpoint
payload	object	Rich checkout context (product details, applied offers, pricing). Alternative to checkout_token for structured data.
expires_at	datetime	When this handoff data expires

Follow-Up Object

Suggestions for future engagement:

Field	Type	Description
suggested_action	string	What the host might do next
data	object	Relevant data for the action
message	string	Optional message to display

Examples

Transaction Handoff

After receiving pending_handoff with type: "transaction":

Request:

{
  "session_id": "sess_abc123",
  "reason": "handoff_transaction",
  "termination_context": {
    "intent": {
      "action": "purchase",
      "product": {
        "type": "flight",
        "flight_number": "DL628"
      }
    }
  }
}

Response:

{
  "session_id": "sess_abc123",
  "terminated": true,
  "acp_handoff": {
    "checkout_url": "https://delta.com/acp/checkout",
    "payload": {
      "session_id": "sess_abc123",
      "flight": "DL628",
      "passenger": {
        "email": "[e-mail]",
        "name": "Jane Smith"
      },
      "applied_offers": ["delta_chatgpt_3313"],
      "price": {
        "amount": 199,
        "currency": "USD"
      }
    },
    "expires_at": "2026-01-18T11:00:00Z"
  }
}

Conversation Complete (No Purchase)

When the conversation naturally ends without a transaction:

Request:

{
  "session_id": "sess_abc123",
  "reason": "handoff_complete"
}

Response:

{
  "session_id": "sess_abc123",
  "terminated": true,
  "follow_up": {
    "suggested_action": "save_for_later",
    "data": {
      "flights_discussed": ["DL628", "DL632"],
      "destination": "BOS",
      "travel_date": "2026-01-27"
    },
    "message": "Let me know if you'd like to revisit Boston flights later!"
  }
}

User Exit

When the user changes topic or explicitly leaves:

Request:

{
  "session_id": "sess_abc123",
  "reason": "user_exit",
  "termination_context": {
    "user_signal": "changed_topic",
    "partial_context": {
      "flights_viewed": ["DL628"],
      "last_topic": "seat selection"
    }
  }
}

Response:

{
  "session_id": "sess_abc123",
  "terminated": true,
  "follow_up": {
    "suggested_action": "remind_later",
    "data": {
      "incomplete_booking": {
        "flight": "DL628",
        "step": "seat_selection"
      }
    }
  }
}

Session Timeout

When the session times out due to inactivity:

Request:

{
  "session_id": "sess_abc123",
  "reason": "session_timeout",
  "termination_context": {
    "last_activity": "2026-01-18T10:25:00Z",
    "timeout_seconds": 300
  }
}

Response:

{
  "session_id": "sess_abc123",
  "terminated": true
}

Host Terminated

When the host ends the session for policy or error reasons:

Request:

{
  "session_id": "sess_abc123",
  "reason": "host_terminated",
  "termination_context": {
    "cause": "user_left_app"
  }
}

Response:

{
  "session_id": "sess_abc123",
  "terminated": true
}

ACP Integration Flow

When the reason is handoff_transaction:

1. Host receives acp_handoff in the termination response
2. Host initiates ACP checkout using the provided checkout_url and checkout_token or payload
3. ACP handles the transaction while maintaining the user’s trust with the host
4. Brand is not the merchant of record - ACP handles payment

Key Points

1. Always terminate sessions - Even if the conversation seems done, call terminate to clean up resources and get follow-up suggestions.

2. ACP handoff data has expiration - The expires_at field indicates how long the checkout context is valid.

3. Follow-up enables re-engagement - Even non-transaction terminations can include suggestions for future engagement.

4. Host maintains trust - Transactions go through ACP, keeping the user’s relationship with the host intact.