Profiles and several sessions

A LanguageModelSession.DynamicProfile picks one Profile each time the model is prompted. Instructions, tools, and the model can change with app state. Only one profile is active in that session. This is not parallel voting.

import FoundationModels
import Observation

@Observable
final class ReviewBoard {
    enum Seat: String { case planner, critic, judge }
    var seat: Seat = .planner
}

struct ReviewProfile: LanguageModelSession.DynamicProfile {
    var board: ReviewBoard

    var body: some LanguageModelSession.DynamicProfile {
        switch board.seat {
        case .planner:
            Profile {
                Instructions("Propose one concrete action. Do not execute it.")
            }
            .model(SystemLanguageModel.default)
        case .critic:
            Profile {
                Instructions("List only concrete risks in the proposed action.")
            }
            .model(SystemLanguageModel.default)
        case .judge:
            Profile {
                Instructions("Approve, reject, or escalate. Reply with one word first: approve, reject, or escalate.")
            }
            .model(SystemLanguageModel.default)
        }
    }
}

let board = ReviewBoard()
let session = LanguageModelSession(profile: ReviewProfile(board: board))

Apple also names two patterns in WWDC26 session 242. Baton-pass stays in one session and changes which profile is active. Phone-a-friend opens a short child session and returns its reply as tool output. Use those names as Apple uses them. Then say what they do in plain words.

Weighted voting needs several independent replies. Create several LanguageModelSession values, each with its own instructions. Do not expect one Dynamic Profile body to produce three concurrent votes. You can still use a profile later for the judge seat.

Read Pause and resume long AI jobs, Stop prompt attacks and leaks, and Talk to tools with MCP if a vote round must pause, or if a specialist prompt might carry an injection.

Next, collect weighted votes in app code.