diff --git a/migrations/0028_ai_usage_status_index.sql b/migrations/0028_ai_usage_status_index.sql
new file mode 100644
index 0000000000..8d9a114bfb
--- /dev/null
+++ b/migrations/0028_ai_usage_status_index.sql
@@ -0,0 +1,6 @@
+-- Covers the daily AI-neuron budget query (sumAiEstimatedNeuronsSince):
+--   SELECT sum(estimated_neurons) FROM ai_usage_events WHERE status = 'ok' AND created_at >= ?
+-- Without this index that aggregate full-scans ai_usage_events, and it runs on every AI review/summary.
+-- Numbered 0028 to avoid colliding with migrations 0026/0027 reserved by the AI-review PR (#652); the
+-- D1 migration runner applies un-applied files in order and tolerates gaps.
+CREATE INDEX IF NOT EXISTS ai_usage_events_status_created_idx ON ai_usage_events (status, created_at);
diff --git a/src/db/schema.ts b/src/db/schema.ts
index 326a4f028d..9d0baa6827 100644
--- a/src/db/schema.ts
+++ b/src/db/schema.ts
@@ -923,5 +923,8 @@ export const aiUsageEvents = sqliteTable(
   (table) => ({
     featureCreated: index("ai_usage_events_feature_created_idx").on(table.feature, table.createdAt),
     actorCreated: index("ai_usage_events_actor_created_idx").on(table.actor, table.createdAt),
+    // Covers the daily-budget query (sumAiEstimatedNeuronsSince): WHERE status='ok' AND created_at >= ?.
+    // Without it that aggregate full-scans ai_usage_events, which runs on every AI review/summary.
+    statusCreated: index("ai_usage_events_status_created_idx").on(table.status, table.createdAt),
   }),
 );
diff --git a/test/unit/ai-usage-index.test.ts b/test/unit/ai-usage-index.test.ts
new file mode 100644
index 0000000000..61de4f065f
--- /dev/null
+++ b/test/unit/ai-usage-index.test.ts
@@ -0,0 +1,23 @@
+import { describe, expect, it } from "vitest";
+import { createTestEnv } from "../helpers/d1";
+
+describe("ai_usage_events budget index", () => {
+  it("creates the (status, created_at) index and the budget query uses it (SEARCH, not SCAN)", async () => {
+    const env = createTestEnv();
+
+    const idx = await env.DB.prepare("SELECT name FROM sqlite_master WHERE type='index' AND name = ?")
+      .bind("ai_usage_events_status_created_idx")
+      .first<{ name: string }>();
+    expect(idx?.name).toBe("ai_usage_events_status_created_idx");
+
+    // sumAiEstimatedNeuronsSince: WHERE status='ok' AND created_at >= ? — must SEARCH via the new index.
+    const plan = await env.DB.prepare(
+      "EXPLAIN QUERY PLAN SELECT coalesce(sum(estimated_neurons),0) FROM ai_usage_events WHERE created_at >= ? AND status = 'ok'",
+    )
+      .bind("2026-01-01T00:00:00.000Z")
+      .all<{ detail: string }>();
+    const detail = (plan.results ?? []).map((row) => row.detail).join(" ");
+    expect(detail).toContain("ai_usage_events_status_created_idx");
+    expect(detail).not.toContain("SCAN ai_usage_events ");
+  });
+});