diff --git a/services/document-updater/scripts/project_notifications.mts b/services/document-updater/scripts/project_notifications.mts
index 65f5aedfbd..46e6b0f5fc 100644
--- a/services/document-updater/scripts/project_notifications.mts
+++ b/services/document-updater/scripts/project_notifications.mts
@@ -1,6 +1,7 @@
 import Settings from '@overleaf/settings'
 import logger from '@overleaf/logger'
 import { createClient } from '@overleaf/redis-wrapper'
+import { promiseMapWithLimit } from '@overleaf/promise-utils'
 import mongodb from '../app/js/mongodb.js'
 import Queue from 'bull'
 import minimist from 'minimist'
@@ -71,6 +72,8 @@ const queueRedisConfig = {
   password: process.env.QUEUES_REDIS_PASSWORD,
 }
 const QUEUE_NAME = 'project-notification'
+const MONGO_IN_BATCH_SIZE = 5000
+const MONGO_BATCH_CONCURRENCY = 5
 const PROGRESS_LOG_INTERVAL_MS = 15_000
 
 const projectNotificationQueue = new Queue(QUEUE_NAME, {
@@ -99,7 +102,7 @@ async function main() {
     `Scan complete: scanned=${stats.scanned}, matched=${stats.matched}, skippedNoCollaborators=${stats.skippedNoCollaborators}, skippedNoTimestamp=${stats.skippedNoTimestamp}, skippedInvalidTimestamp=${stats.skippedInvalidTimestamp}, skippedNoProjectId=${stats.skippedNoProjectId}`
   )
   console.log(
-    `Collaborator lookups: cacheHitWithCollaborators=${stats.collaboratorCacheHitWithCollaborators}, cacheHitNoCollaborators=${stats.collaboratorCacheHitNoCollaborators}, cacheMissWithCollaborators=${stats.collaboratorCacheMissWithCollaborators}, cacheMissNoCollaborators=${stats.collaboratorCacheMissNoCollaborators}`
+    `Collaborator lookups: cacheHitWithCollaborators=${stats.collaboratorCacheHitWithCollaborators}, cacheHitNoCollaborators=${stats.collaboratorCacheHitNoCollaborators}, cacheMissWithCollaborators=${stats.collaboratorCacheMissWithCollaborators}, cacheMissNoCollaborators=${stats.collaboratorCacheMissNoCollaborators}, mongoQueries=${stats.collaboratorMongoQueries}`
   )
 
   if (dryRun) {
@@ -182,55 +185,87 @@ type ProjectNotification = {
 }
 
 /**
- * Check if a project has any collaborators (excluding owner)
- * Uses Redis caching with 1-2 hour randomized expiration to avoid repeated MongoDB queries
+ * For a batch of project IDs, return the set of those that have collaborators.
+ * Uses Redis caching with 1-2 hour randomized expiration to avoid repeated MongoDB queries.
+ * Performs a single mget for cache hits, a single $in find for cache misses,
+ * and a single pipelined setex to write back the results.
  */
-async function projectHasCollaborators(
-  projectId: string,
+async function getProjectsWithCollaborators(
+  projectIds: string[],
   stats: NotificationStats
-): Promise<boolean> {
-  // Check Redis cache first
-  const cacheKey = `ProjectHasCollaborators:{${projectId}}`
-  const cachedResult = await redisClient.get(cacheKey)
+): Promise<Set<string>> {
+  const projectsWithCollaborators = new Set<string>()
+  if (projectIds.length === 0) return projectsWithCollaborators
 
-  if (cachedResult !== null) {
-    if (cachedResult === '1') {
+  const cacheKeys = projectIds.map(id => `ProjectHasCollaborators:{${id}}`)
+  const cached = await redisClient.mget(cacheKeys)
+
+  const projectsNeedingMongoLookup: string[] = []
+  for (const [i, id] of projectIds.entries()) {
+    if (cached[i] === '1') {
       stats.collaboratorCacheHitWithCollaborators++
-    } else {
+      projectsWithCollaborators.add(id)
+    } else if (cached[i] === '0') {
       stats.collaboratorCacheHitNoCollaborators++
+    } else {
+      projectsNeedingMongoLookup.push(id)
     }
-    return cachedResult === '1'
   }
 
-  // Cache miss - query MongoDB
-  const hasCollaborators = await db.projects.findOne(
-    {
-      _id: new ObjectId(projectId),
-      $or: [
-        { 'collaberator_refs.0': { $exists: true } }, // check that first element in array exists
-        { 'readOnly_refs.0': { $exists: true } },
-        { 'reviewer_refs.0': { $exists: true } },
-        { 'tokenAccessReadAndWrite_refs.0': { $exists: true } },
-        { 'tokenAccessReadOnly_refs.0': { $exists: true } },
-      ],
-    },
-    { projection: { _id: 1 }, readPreference: READ_PREFERENCE_SECONDARY }
+  if (projectsNeedingMongoLookup.length === 0) return projectsWithCollaborators
+
+  const batches: string[][] = []
+  for (
+    let i = 0;
+    i < projectsNeedingMongoLookup.length;
+    i += MONGO_IN_BATCH_SIZE
+  ) {
+    batches.push(projectsNeedingMongoLookup.slice(i, i + MONGO_IN_BATCH_SIZE))
+  }
+
+  const batchResults = await promiseMapWithLimit(
+    MONGO_BATCH_CONCURRENCY,
+    batches,
+    async (batch: string[]) => {
+      stats.collaboratorMongoQueries++
+      return await db.projects
+        .find(
+          {
+            _id: { $in: batch.map(id => new ObjectId(id)) },
+            $or: [
+              { 'collaberator_refs.0': { $exists: true } },
+              { 'readOnly_refs.0': { $exists: true } },
+              { 'reviewer_refs.0': { $exists: true } },
+              { 'tokenAccessReadAndWrite_refs.0': { $exists: true } },
+              { 'tokenAccessReadOnly_refs.0': { $exists: true } },
+            ],
+          },
+          { projection: { _id: 1 }, readPreference: READ_PREFERENCE_SECONDARY }
+        )
+        .toArray()
+    }
   )
 
-  // Use random TTL between 1-2 hours (3600-7200 seconds) to smooth out cache expiration
-  const randomTTL = 3600 + Math.floor(Math.random() * 3600)
+  const positives = new Set(
+    batchResults.flatMap(docs => docs.map(d => d._id.toString()))
+  )
 
-  if (hasCollaborators === null) {
-    // Cache negative result (no collaborators or project not found)
-    stats.collaboratorCacheMissNoCollaborators++
-    await redisClient.setex(cacheKey, randomTTL, '0')
-    return false
+  const pipeline = redisClient.pipeline()
+  for (const id of projectsNeedingMongoLookup) {
+    // Use random TTL between 1-2 hours (3600-7200 seconds) to smooth out cache expiration
+    const ttl = 3600 + Math.floor(Math.random() * 3600)
+    const hit = positives.has(id)
+    if (hit) {
+      stats.collaboratorCacheMissWithCollaborators++
+      projectsWithCollaborators.add(id)
+    } else {
+      stats.collaboratorCacheMissNoCollaborators++
+    }
+    pipeline.setex(`ProjectHasCollaborators:{${id}}`, ttl, hit ? '1' : '0')
   }
+  await pipeline.exec()
 
-  // Cache the result in Redis
-  stats.collaboratorCacheMissWithCollaborators++
-  await redisClient.setex(cacheKey, randomTTL, hasCollaborators ? '1' : '0')
-  return true
+  return projectsWithCollaborators
 }
 
 /**
@@ -247,6 +282,7 @@ type NotificationStats = {
   collaboratorCacheHitNoCollaborators: number
   collaboratorCacheMissWithCollaborators: number
   collaboratorCacheMissNoCollaborators: number
+  collaboratorMongoQueries: number
 }
 
 async function getProjectsToNotify(): Promise<{
@@ -269,6 +305,7 @@ async function getProjectsToNotify(): Promise<{
     collaboratorCacheHitNoCollaborators: 0,
     collaboratorCacheMissWithCollaborators: 0,
     collaboratorCacheMissNoCollaborators: 0,
+    collaboratorMongoQueries: 0,
   }
   let lastProgressLog = Date.now()
 
@@ -287,6 +324,8 @@ async function getProjectsToNotify(): Promise<{
 
         const timestamps = await redisClient.mget(keys)
 
+        // Extract valid (projectId, timestamp) pairs from this batch
+        const candidates: ProjectNotification[] = []
         for (const [index, key] of keys.entries()) {
           stats.scanned++
           const projectId = extractProjectId(key as string)
@@ -304,15 +343,6 @@ async function getProjectsToNotify(): Promise<{
             continue
           }
 
-          const hasCollaborators = await projectHasCollaborators(
-            projectId,
-            stats
-          )
-          if (!hasCollaborators) {
-            stats.skippedNoCollaborators++
-            continue
-          }
-
           const numericTimestamp = parseInt(timestamp, 10)
           if (Number.isNaN(numericTimestamp)) {
             stats.skippedInvalidTimestamp++
@@ -322,8 +352,22 @@ async function getProjectsToNotify(): Promise<{
             continue
           }
 
+          candidates.push({ projectId, timestamp })
+        }
+
+        // Bulk-check collaborators for the whole batch
+        const projectsWithCollaborators = await getProjectsWithCollaborators(
+          candidates.map(c => c.projectId),
+          stats
+        )
+
+        for (const c of candidates) {
+          if (!projectsWithCollaborators.has(c.projectId)) {
+            stats.skippedNoCollaborators++
+            continue
+          }
           stats.matched++
-          projects.push({ projectId, timestamp })
+          projects.push(c)
         }
 
         if (Date.now() - lastProgressLog >= PROGRESS_LOG_INTERVAL_MS) {