diff --git a/.changeset/dull-carrots-bow.md b/.changeset/dull-carrots-bow.md
new file mode 100644
index 0000000000..950c823735
--- /dev/null
+++ b/.changeset/dull-carrots-bow.md
@@ -0,0 +1,5 @@
+---
+"@hyperdx/api": patch
+---
+
+Disable mongoose autoIndex in check-alerts worker to prevent MongoExpiredSessionError
diff --git a/packages/api/src/models/index.ts b/packages/api/src/models/index.ts
index 3e932d006a..1779e3dc41 100644
--- a/packages/api/src/models/index.ts
+++ b/packages/api/src/models/index.ts
@@ -51,7 +51,7 @@ mongoose.connection.on('reconnectFailed', () => {
   logger.error('Failed to reconnect to MongoDB');
 });
 
-export const connectDB = async () => {
+export const connectDB = async (options?: mongoose.ConnectOptions) => {
   // breadcrumbs for future greppers: aws4 is included as a dependency of the api so that
   // users can use AWS auth in their mongo connection string here, e.g.
   // mongodb+srv://blahblah...mongodb.net/hyperdx?authSource=%24external&authMechanism=MONGODB-AWS
@@ -61,6 +61,7 @@ export const connectDB = async () => {
   await mongoose.connect(config.MONGO_URI, {
     heartbeatFrequencyMS: 10000, // retry failed heartbeats
     maxPoolSize: 100, // 5 nodes -> max 1000 connections
+    ...options,
   });
 };
 
diff --git a/packages/api/src/tasks/checkAlerts/providers/default.ts b/packages/api/src/tasks/checkAlerts/providers/default.ts
index d14f456834..4075b09560 100644
--- a/packages/api/src/tasks/checkAlerts/providers/default.ts
+++ b/packages/api/src/tasks/checkAlerts/providers/default.ts
@@ -274,7 +274,12 @@ async function loadAlert(
 
 export default class DefaultAlertProvider implements AlertProvider {
   async init() {
-    await Promise.all([connectDB()]);
+    // The check-alerts worker only reads from MongoDB and never needs to
+    // ensure indexes exist (the API service owns that). Disabling autoIndex
+    // prevents background createIndexes calls from racing the short-lived
+    // connection close (which sends endSessions), surfaced as
+    // MongoExpiredSessionError on mongodb.createIndexes spans.
+    await Promise.all([connectDB({ autoIndex: false })]);
   }
 
   async asyncDispose() {