diff --git a/packages/kal-backend/src/lib/request-log-service.ts b/packages/kal-backend/src/lib/request-log-service.ts
index 4933395..1b151c3 100644
--- a/packages/kal-backend/src/lib/request-log-service.ts
+++ b/packages/kal-backend/src/lib/request-log-service.ts
@@ -18,6 +18,9 @@ export interface ApiRequestLog {
   requestId: string;
   timestamp: Date;
 
+  // TTL — per-doc expiration (429s: 30 days, success: 90 days)
+  expiresAt: Date;
+
   // User/Auth info
   userId: string | null;
   apiKeyPrefix: string | null;
diff --git a/packages/kal-backend/src/middleware/api-request-logger.ts b/packages/kal-backend/src/middleware/api-request-logger.ts
index 738f417..18446a9 100644
--- a/packages/kal-backend/src/middleware/api-request-logger.ts
+++ b/packages/kal-backend/src/middleware/api-request-logger.ts
@@ -139,10 +139,17 @@ export function createApiRequestLogger(options: LoggerOptions = {}) {
         error = `HTTP ${statusCode}`;
       }
 
+      // Per-doc TTL: 429 rate-limited requests expire in 30 days, others in 90 days
+      const TTL_SUCCESS_MS = 90 * 24 * 60 * 60 * 1000;
+      const TTL_RATE_LIMITED_MS = 30 * 24 * 60 * 60 * 1000;
+      const ttlMs = statusCode === 429 ? TTL_RATE_LIMITED_MS : TTL_SUCCESS_MS;
+      const now = new Date();
+
       // Build log entry
       const logEntry = {
         requestId,
-        timestamp: new Date(),
+        timestamp: now,
+        expiresAt: new Date(now.getTime() + ttlMs),
         userId,
         apiKeyPrefix,
         type,
diff --git a/packages/kal-db/migrations/20260411000003_per_doc_ttl_request_logs.js b/packages/kal-db/migrations/20260411000003_per_doc_ttl_request_logs.js
new file mode 100644
index 0000000..20a5c9d
--- /dev/null
+++ b/packages/kal-db/migrations/20260411000003_per_doc_ttl_request_logs.js
@@ -0,0 +1,79 @@
+/**
+ * Migration: Per-document TTL for api_request_logs
+ *
+ * Replaces the fixed 90-day TTL index on `timestamp` with a TTL index
+ * on `expiresAt` (expireAfterSeconds: 0). Each document sets its own
+ * expiration:
+ *   - 429 rate-limited requests: 30 days
+ *   - All other requests: 90 days
+ *
+ * This reduces storage for abusive/rate-limited traffic while keeping
+ * normal request logs for the full 90-day window.
+ */
+
+export const up = async (db, _client) => {
+  const col = db.collection("api_request_logs");
+
+  // Drop the old fixed-TTL index on timestamp
+  await col.dropIndex("ttl_90_days").catch(() => {
+    console.log("ℹ️  ttl_90_days index not found, skipping drop");
+  });
+  console.log("✅ Dropped old ttl_90_days index");
+
+  // Create new TTL index on expiresAt (expireAfterSeconds: 0 means
+  // "delete when the expiresAt date is reached")
+  await col.createIndex(
+    { expiresAt: 1 },
+    { expireAfterSeconds: 0, name: "ttl_per_doc" }
+  );
+  console.log("✅ Created per-document TTL index on expiresAt");
+
+  // Backfill expiresAt for existing documents that don't have it yet
+  // 429 requests get 30 days from their timestamp, others get 90 days
+  const TTL_SUCCESS_S = 90 * 24 * 60 * 60;
+  const TTL_RATE_LIMITED_S = 30 * 24 * 60 * 60;
+
+  // Rate-limited docs (statusCode 429)
+  const rateLimitedResult = await col.updateMany(
+    { statusCode: 429, expiresAt: { $exists: false } },
+    [
+      {
+        $set: {
+          expiresAt: {
+            $dateAdd: { startDate: "$timestamp", unit: "second", amount: TTL_RATE_LIMITED_S },
+          },
+        },
+      },
+    ]
+  );
+  console.log(`✅ Backfilled ${rateLimitedResult.modifiedCount} rate-limited docs (30-day TTL)`);
+
+  // All other docs
+  const successResult = await col.updateMany(
+    { statusCode: { $ne: 429 }, expiresAt: { $exists: false } },
+    [
+      {
+        $set: {
+          expiresAt: {
+            $dateAdd: { startDate: "$timestamp", unit: "second", amount: TTL_SUCCESS_S },
+          },
+        },
+      },
+    ]
+  );
+  console.log(`✅ Backfilled ${successResult.modifiedCount} normal docs (90-day TTL)`);
+};
+
+export const down = async (db, _client) => {
+  const col = db.collection("api_request_logs");
+
+  // Drop per-doc TTL index
+  await col.dropIndex("ttl_per_doc").catch(() => {});
+
+  // Restore the original fixed 90-day TTL on timestamp
+  await col.createIndex(
+    { timestamp: 1 },
+    { expireAfterSeconds: 7776000, name: "ttl_90_days" }
+  );
+  console.log("✅ Restored fixed 90-day TTL index on timestamp");
+};