diff --git a/server/src/main/java/org/elasticsearch/index/codec/vectors/DefaultIVFVectorsWriter.java b/server/src/main/java/org/elasticsearch/index/codec/vectors/DefaultIVFVectorsWriter.java
index 726e84605157a..f34ad071b6ba0 100644
--- a/server/src/main/java/org/elasticsearch/index/codec/vectors/DefaultIVFVectorsWriter.java
+++ b/server/src/main/java/org/elasticsearch/index/codec/vectors/DefaultIVFVectorsWriter.java
@@ -17,8 +17,11 @@
 import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.store.IndexOutput;
+import org.apache.lucene.util.LongValues;
 import org.apache.lucene.util.VectorUtil;
 import org.apache.lucene.util.hnsw.IntToIntFunction;
+import org.apache.lucene.util.packed.PackedInts;
+import org.apache.lucene.util.packed.PackedLongValues;
 import org.elasticsearch.index.codec.vectors.cluster.HierarchicalKMeans;
 import org.elasticsearch.index.codec.vectors.cluster.KMeansResult;
 import org.elasticsearch.logging.LogManager;
@@ -46,7 +49,7 @@ public DefaultIVFVectorsWriter(SegmentWriteState state, FlatVectorsWriter rawVec
     }
 
     @Override
-    long[] buildAndWritePostingsLists(
+    LongValues buildAndWritePostingsLists(
         FieldInfo fieldInfo,
         CentroidSupplier centroidSupplier,
         FloatVectorValues floatVectorValues,
@@ -81,7 +84,7 @@ long[] buildAndWritePostingsLists(
             }
         }
         // write the posting lists
-        final long[] offsets = new long[centroidSupplier.size()];
+        final PackedLongValues.Builder offsets = PackedLongValues.monotonicBuilder(PackedInts.COMPACT);
         DocIdsWriter docIdsWriter = new DocIdsWriter();
         DiskBBQBulkWriter bulkWriter = new DiskBBQBulkWriter.OneBitDiskBBQBulkWriter(ES91OSQVectorsScorer.BULK_SIZE, postingsOutput);
         OnHeapQuantizedVectors onHeapQuantizedVectors = new OnHeapQuantizedVectors(
@@ -93,7 +96,7 @@ long[] buildAndWritePostingsLists(
             float[] centroid = centroidSupplier.centroid(c);
             int[] cluster = assignmentsByCluster[c];
             // TODO align???
-            offsets[c] = postingsOutput.getFilePointer();
+            offsets.add(postingsOutput.getFilePointer());
             int size = cluster.length;
             postingsOutput.writeVInt(size);
             postingsOutput.writeInt(Float.floatToIntBits(VectorUtil.dotProduct(centroid, centroid)));
@@ -109,11 +112,11 @@ long[] buildAndWritePostingsLists(
             printClusterQualityStatistics(assignmentsByCluster);
         }
 
-        return offsets;
+        return offsets.build();
     }
 
     @Override
-    long[] buildAndWritePostingsLists(
+    LongValues buildAndWritePostingsLists(
         FieldInfo fieldInfo,
         CentroidSupplier centroidSupplier,
         FloatVectorValues floatVectorValues,
@@ -199,7 +202,7 @@ long[] buildAndWritePostingsLists(
         }
         // now we can read the quantized vectors from the temporary file
         try (IndexInput quantizedVectorsInput = mergeState.segmentInfo.dir.openInput(quantizedVectorsTempName, IOContext.DEFAULT)) {
-            final long[] offsets = new long[centroidSupplier.size()];
+            final PackedLongValues.Builder offsets = PackedLongValues.monotonicBuilder(PackedInts.COMPACT);
             OffHeapQuantizedVectors offHeapQuantizedVectors = new OffHeapQuantizedVectors(
                 quantizedVectorsInput,
                 fieldInfo.getVectorDimension()
@@ -210,9 +213,9 @@ long[] buildAndWritePostingsLists(
                 float[] centroid = centroidSupplier.centroid(c);
                 int[] cluster = assignmentsByCluster[c];
                 boolean[] isOverspill = isOverspillByCluster[c];
-                // TODO align???
-                offsets[c] = postingsOutput.getFilePointer();
+                offsets.add(postingsOutput.getFilePointer());
                 int size = cluster.length;
+                // TODO align???
                 postingsOutput.writeVInt(size);
                 postingsOutput.writeInt(Float.floatToIntBits(VectorUtil.dotProduct(centroid, centroid)));
                 offHeapQuantizedVectors.reset(size, ord -> isOverspill[ord], ord -> cluster[ord]);
@@ -226,7 +229,7 @@ long[] buildAndWritePostingsLists(
             if (logger.isDebugEnabled()) {
                 printClusterQualityStatistics(assignmentsByCluster);
             }
-            return offsets;
+            return offsets.build();
         }
     }
 
@@ -270,7 +273,7 @@ void writeCentroids(
         FieldInfo fieldInfo,
         CentroidSupplier centroidSupplier,
         float[] globalCentroid,
-        long[] offsets,
+        LongValues offsets,
         IndexOutput centroidOutput
     ) throws IOException {
 
@@ -302,7 +305,7 @@ void writeCentroids(
             // write the centroids
             centroidOutput.writeBytes(buffer.array(), buffer.array().length);
             // write the offset of this posting list
-            centroidOutput.writeLong(offsets[i]);
+            centroidOutput.writeLong(offsets.get(i));
         }
     }
 
diff --git a/server/src/main/java/org/elasticsearch/index/codec/vectors/IVFVectorsWriter.java b/server/src/main/java/org/elasticsearch/index/codec/vectors/IVFVectorsWriter.java
index f828c96f7a9e1..149db2eb96b83 100644
--- a/server/src/main/java/org/elasticsearch/index/codec/vectors/IVFVectorsWriter.java
+++ b/server/src/main/java/org/elasticsearch/index/codec/vectors/IVFVectorsWriter.java
@@ -28,6 +28,7 @@
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.store.IndexOutput;
 import org.apache.lucene.store.RandomAccessInput;
+import org.apache.lucene.util.LongValues;
 import org.apache.lucene.util.VectorUtil;
 import org.elasticsearch.core.IOUtils;
 import org.elasticsearch.core.SuppressForbidden;
@@ -126,11 +127,11 @@ abstract void writeCentroids(
         FieldInfo fieldInfo,
         CentroidSupplier centroidSupplier,
         float[] globalCentroid,
-        long[] centroidOffset,
+        LongValues centroidOffset,
         IndexOutput centroidOutput
     ) throws IOException;
 
-    abstract long[] buildAndWritePostingsLists(
+    abstract LongValues buildAndWritePostingsLists(
         FieldInfo fieldInfo,
         CentroidSupplier centroidSupplier,
         FloatVectorValues floatVectorValues,
@@ -139,7 +140,7 @@ abstract long[] buildAndWritePostingsLists(
         int[] overspillAssignments
     ) throws IOException;
 
-    abstract long[] buildAndWritePostingsLists(
+    abstract LongValues buildAndWritePostingsLists(
         FieldInfo fieldInfo,
         CentroidSupplier centroidSupplier,
         FloatVectorValues floatVectorValues,
@@ -160,7 +161,7 @@ abstract CentroidSupplier createCentroidSupplier(
     public final void flush(int maxDoc, Sorter.DocMap sortMap) throws IOException {
         rawVectorDelegate.flush(maxDoc, sortMap);
         for (FieldWriter fieldWriter : fieldWriters) {
-            float[] globalCentroid = new float[fieldWriter.fieldInfo.getVectorDimension()];
+            final float[] globalCentroid = new float[fieldWriter.fieldInfo.getVectorDimension()];
             // build a float vector values with random access
             final FloatVectorValues floatVectorValues = getFloatVectorValues(fieldWriter.fieldInfo, fieldWriter.delegate, maxDoc);
             // build centroids
@@ -168,7 +169,7 @@ public final void flush(int maxDoc, Sorter.DocMap sortMap) throws IOException {
             // wrap centroids with a supplier
             final CentroidSupplier centroidSupplier = new OnHeapCentroidSupplier(centroidAssignments.centroids());
             // write posting lists
-            final long[] offsets = buildAndWritePostingsLists(
+            final LongValues offsets = buildAndWritePostingsLists(
                 fieldWriter.fieldInfo,
                 centroidSupplier,
                 floatVectorValues,
@@ -176,9 +177,8 @@ public final void flush(int maxDoc, Sorter.DocMap sortMap) throws IOException {
                 centroidAssignments.assignments(),
                 centroidAssignments.overspillAssignments()
             );
-            assert offsets.length == centroidSupplier.size();
-            final long centroidOffset = ivfCentroids.alignFilePointer(Float.BYTES);
             // write centroids
+            final long centroidOffset = ivfCentroids.alignFilePointer(Float.BYTES);
             writeCentroids(fieldWriter.fieldInfo, centroidSupplier, globalCentroid, offsets, ivfCentroids);
             final long centroidLength = ivfCentroids.getFilePointer() - centroidOffset;
             // write meta file
@@ -338,7 +338,7 @@ private void mergeOneFieldIVF(FieldInfo fieldInfo, MergeState mergeState) throws
                         calculatedGlobalCentroid
                     );
                     // write posting lists
-                    final long[] offsets = buildAndWritePostingsLists(
+                    final LongValues offsets = buildAndWritePostingsLists(
                         fieldInfo,
                         centroidSupplier,
                         floatVectorValues,
@@ -347,9 +347,8 @@ private void mergeOneFieldIVF(FieldInfo fieldInfo, MergeState mergeState) throws
                         assignments,
                         overspillAssignments
                     );
-                    assert offsets.length == centroidSupplier.size();
-                    centroidOffset = ivfCentroids.alignFilePointer(Float.BYTES);
                     // write centroids
+                    centroidOffset = ivfCentroids.alignFilePointer(Float.BYTES);
                     writeCentroids(fieldInfo, centroidSupplier, calculatedGlobalCentroid, offsets, ivfCentroids);
                     centroidLength = ivfCentroids.getFilePointer() - centroidOffset;
                     // write meta