diff --git a/packages/contracts/src/arena.ts b/packages/contracts/src/arena.ts
index 9855e55..531fc09 100644
--- a/packages/contracts/src/arena.ts
+++ b/packages/contracts/src/arena.ts
@@ -1,10 +1,23 @@
 /** Arena types — single source of truth for cross-app Arena wire contracts. */
 
+import { z } from 'zod';
+
 export type BattleType = 'coding' | 'qa';
 export type BattleStatus = 'pending' | 'running' | 'completed' | 'failed' | 'cancelled';
 export type ContestantStatus = 'queued' | 'running' | 'done' | 'error';
 export type ContestantLane = 'local' | 'cloud';
 
+export const TokenBreakdownSchema = z.object({
+  system: z.number().int().nonnegative(),
+  user: z.number().int().nonnegative(),
+  assistant: z.number().int().nonnegative(),
+  tools: z.number().int().nonnegative(),
+  reasoning: z.number().int().nonnegative(),
+  total: z.number().int().nonnegative(),
+});
+
+export type TokenBreakdown = z.infer<typeof TokenBreakdownSchema>;
+
 // Pane state — carried on the WorkspacePane row, mirrors OrchestratorState.
 export interface ArenaState {
   battle_id: string;
@@ -38,6 +51,7 @@ export interface ContestantShape {
   duration_ms: number | null;
   tokens_per_sec: number | null;
   cost_tokens: number | null;
+  token_breakdown: TokenBreakdown | null;
   result_path: string | null;
   error: string | null;
   created_at: string;