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Not every game is strictly turn-based. Bidding rounds, planning phases, and games like paper-scissors-rock let multiple players act at the same time. Gamekit’s phase-level activePlayers plus move.stay express this cleanly.

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The idea

  1. Declare a phase where multiple seats are active.
  2. Each player’s move does not end the turn; it records their input and returns move.stay({ ... }).
  3. When everyone has submitted, the last submission transitions (move.endTurn or move.goto).

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Worked example

From examples/simultaneous-moves/paper-scissors-rock: 
const PLAYERS = ["0", "1", "2"] as const;

export const paperScissorsRock = defineGame({
  maxPlayers: 3,
  setup: ({ match }) => ({
    round: 1,
    scores: roster.record(match, 0),
    submissions: createHiddenChoices(),
    // ...
  }),
  initialPhase: "plan",
  phases: {
    plan: {
      activePlayers: ({ G }) => PLAYERS.filter((id) => G.submissions[id] === null),
      label: ({ G }) => `Round ${G.round}`,
    },
  },
  moves: ({ move }) => ({
    submitChoice: move<PaperScissorsRockChoice>({
      run({ G, args, move, player }) {
        const submissions = { ...G.submissions, [player.id]: args };
        const allSubmitted = PLAYERS.every((id) => submissions[id] !== null);

        if (!allSubmitted) {
          return move.stay({ submissions });
        }

        const outcome = resolveRoundOutcome(submissions);
        const scores = applyWins(G.scores, outcome.winners);

        return move.endTurn({
          lastOutcome: outcome,
          lastRevealed: submissions,
          round: G.round + 1,
          scores,
          submissions: createHiddenChoices(),
        });
      },
    }),
  }),
});
Three things to notice:
  1. activePlayers filters by “has not submitted yet.” Players who already submitted are no longer active, so the engine rejects their retries with inactive_player.
  2. move.stay records one submission without ending the turn. The turn counter does not advance; the phase stays the same.
  3. The last submission triggers the resolution. When allSubmitted is true, the move returns move.endTurn with the next round’s state, advancing the turn counter.

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Hide other players’ submissions

Submissions are secret until everyone has committed. That is a hidden-info pattern, so use views.player: 
views: {
  player: ({ G }, player) => ({
    lastOutcome: G.lastOutcome,
    lastRevealed: G.lastRevealed,        // shown after resolution
    mySubmission: G.submissions[player.id] ?? null,  // only your own
    round: G.round,
    scores: G.scores,
  }),
  public: ({ G }) => ({
    // no `submissions`, no `mySubmission`
    submittedCount: PLAYERS.filter((id) => G.submissions[id] !== null).length,
    lastOutcome: G.lastOutcome,
    lastRevealed: G.lastRevealed,
    round: G.round,
    scores: G.scores,
  }),
},

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What about deadlines?

If you want a timer that forces resolution, enqueue a tick event from the first submission and use context.now to decide when it fires. The engine records now in the replay, so timer-driven transitions stay deterministic. For stricter deadline handling, use @openturn/core’s deadline.after(context, durationMs) to compute a fixed target timestamp, and store it in G. Moves then compare context.now to G.roundDeadline.