diff --git a/CRR/ReplicationStatusUpdater.js b/CRR/ReplicationStatusUpdater.js
index c1a0495f..6216ff40 100644
--- a/CRR/ReplicationStatusUpdater.js
+++ b/CRR/ReplicationStatusUpdater.js
@@ -1,3 +1,4 @@
+const crypto = require('crypto');
 const {
     doWhilst, eachSeries, eachLimit, waterfall,
 } = require('async');
@@ -72,6 +73,14 @@ class ReplicationStatusUpdater {
         this.forceUsingConfiguration = forceUsingConfiguration;
         this.log = log;
 
+        // Random replicationGroupId (7 chars) and instanceId (6 chars) for
+        // microVersionId generation: this tool bypasses CloudServer's
+        // configured values, so per-instance random tokens prevent
+        // collisions with concurrent writers. Sizes match LENGTH_RG and
+        // LENGTH_ID in arsenal's VersionID module.
+        this.replicationGroupId = crypto.randomBytes(4).toString('hex').slice(0, 7);
+        this.instanceId = crypto.randomBytes(3).toString('hex').slice(0, 6);
+
         this._setupClients();
 
         this.logProgressInterval = setInterval(this._logProgress.bind(this), LOG_PROGRESS_INTERVAL_MS);
@@ -193,7 +202,7 @@ class ReplicationStatusUpdater {
                     return process.nextTick(next);
                 }
 
-                objMD.updateMicroVersionId();
+                objMD.updateMicroVersionId(this.instanceId, this.replicationGroupId);
                 const md = objMD.getSerialized();
                 return this.cloudserverclient.putMetadata({
                     Bucket: bucket,
diff --git a/package.json b/package.json
index a3f63fa4..ba942c8c 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "s3utils",
-  "version": "1.18.0",
+  "version": "1.19.0",
   "engines": {
     "node": ">= 22"
   },