diff --git a/src/main/java/org/opensearch/knn/index/codec/KNN10010Codec/KNN10010Codec.java b/src/main/java/org/opensearch/knn/index/codec/KNN10010Codec/KNN10010Codec.java
index 73371bb61..acec0fa7f 100644
--- a/src/main/java/org/opensearch/knn/index/codec/KNN10010Codec/KNN10010Codec.java
+++ b/src/main/java/org/opensearch/knn/index/codec/KNN10010Codec/KNN10010Codec.java
@@ -104,6 +104,11 @@ private StoredFieldsFormat getStoredFieldsFormat() {
             }
             return null;
         }));
-        return new DerivedSourceStoredFieldsFormat(delegate.storedFieldsFormat(), derivedSourceReadersSupplier, mapperService);
+        return new DerivedSourceStoredFieldsFormat(
+            delegate.storedFieldsFormat(),
+            derivedSourceReadersSupplier,
+            mapperService,
+            delegate.getName()
+        );
     }
 }
diff --git a/src/main/java/org/opensearch/knn/index/codec/KNN9120Codec/DerivedSourceStoredFieldsFormat.java b/src/main/java/org/opensearch/knn/index/codec/KNN9120Codec/DerivedSourceStoredFieldsFormat.java
index e60b82b2e..109431d08 100644
--- a/src/main/java/org/opensearch/knn/index/codec/KNN9120Codec/DerivedSourceStoredFieldsFormat.java
+++ b/src/main/java/org/opensearch/knn/index/codec/KNN9120Codec/DerivedSourceStoredFieldsFormat.java
@@ -6,6 +6,7 @@
 package org.opensearch.knn.index.codec.KNN9120Codec;
 
 import lombok.AllArgsConstructor;
+import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.StoredFieldsFormat;
 import org.apache.lucene.codecs.StoredFieldsReader;
 import org.apache.lucene.codecs.StoredFieldsWriter;
@@ -32,15 +33,26 @@
 @AllArgsConstructor
 public class DerivedSourceStoredFieldsFormat extends StoredFieldsFormat {
 
+    private static final String DELEGATE_CODEC_KEY = "knn_delegate_codec";
+
     private final StoredFieldsFormat delegate;
     private final DerivedSourceReadersSupplier derivedSourceReadersSupplier;
     // IMPORTANT Do not rely on this for the reader, it will be null if SPI is used
     @Nullable
     private final MapperService mapperService;
+    // IMPORTANT Do not rely on this for the reader, it will be null if SPI is used
+    @Nullable
+    private final String delegateCodecName;
 
     @Override
     public StoredFieldsReader fieldsReader(Directory directory, SegmentInfo segmentInfo, FieldInfos fieldInfos, IOContext ioContext)
         throws IOException {
+        StoredFieldsFormat delegateFromWriting = delegate;
+        if (segmentInfo.getAttribute(DELEGATE_CODEC_KEY) != null) {
+            String delegateCodecName = segmentInfo.getAttribute(DELEGATE_CODEC_KEY);
+            delegateFromWriting = Codec.forName(delegateCodecName).storedFieldsFormat();
+        }
+
         List<FieldInfo> derivedVectorFields = null;
         for (FieldInfo fieldInfo : fieldInfos) {
             if (DERIVED_VECTOR_FIELD_ATTRIBUTE_TRUE_VALUE.equals(fieldInfo.attributes().get(DERIVED_VECTOR_FIELD_ATTRIBUTE_KEY))) {
@@ -53,10 +65,10 @@ public StoredFieldsReader fieldsReader(Directory directory, SegmentInfo segmentI
         }
         // If no fields have it enabled, we can just short-circuit and return the delegate's fieldReader
         if (derivedVectorFields == null || derivedVectorFields.isEmpty()) {
-            return delegate.fieldsReader(directory, segmentInfo, fieldInfos, ioContext);
+            return delegateFromWriting.fieldsReader(directory, segmentInfo, fieldInfos, ioContext);
         }
         return new DerivedSourceStoredFieldsReader(
-            delegate.fieldsReader(directory, segmentInfo, fieldInfos, ioContext),
+            delegateFromWriting.fieldsReader(directory, segmentInfo, fieldInfos, ioContext),
             derivedVectorFields,
             derivedSourceReadersSupplier,
             new SegmentReadState(directory, segmentInfo, fieldInfos, ioContext)
@@ -65,6 +77,24 @@ public StoredFieldsReader fieldsReader(Directory directory, SegmentInfo segmentI
 
     @Override
     public StoredFieldsWriter fieldsWriter(Directory directory, SegmentInfo segmentInfo, IOContext ioContext) throws IOException {
+        // We write the delegate codec name into the segmentInfo attributes so that we can read it when loading the
+        // codec from SPI.
+        // This is similar to whats done in
+        // https://github.com/opensearch-project/custom-codecs/blob/2.19.0.0/src/main/java/org/opensearch/index/codec/customcodecs/Lucene912CustomStoredFieldsFormat.java#L95-L100
+        String previous = segmentInfo.putAttribute(DELEGATE_CODEC_KEY, delegateCodecName);
+        if (previous != null && previous.equals(delegateCodecName) == false) {
+            throw new IllegalStateException(
+                "found existing value for "
+                    + DELEGATE_CODEC_KEY
+                    + " for segment: "
+                    + segmentInfo.name
+                    + " old = "
+                    + previous
+                    + ", new = "
+                    + delegateCodecName
+            );
+        }
+
         StoredFieldsWriter delegateWriter = delegate.fieldsWriter(directory, segmentInfo, ioContext);
         if (mapperService != null && KNNSettings.isKNNDerivedSourceEnabled(mapperService.getIndexSettings().getSettings())) {
             List<String> vectorFieldTypes = new ArrayList<>();
diff --git a/src/main/java/org/opensearch/knn/index/codec/backward_codecs/KNN9120Codec/KNN9120Codec.java b/src/main/java/org/opensearch/knn/index/codec/backward_codecs/KNN9120Codec/KNN9120Codec.java
index 375b9fe48..ecd02705b 100644
--- a/src/main/java/org/opensearch/knn/index/codec/backward_codecs/KNN9120Codec/KNN9120Codec.java
+++ b/src/main/java/org/opensearch/knn/index/codec/backward_codecs/KNN9120Codec/KNN9120Codec.java
@@ -100,6 +100,11 @@ private StoredFieldsFormat getStoredFieldsFormat() {
             }
             return null;
         }));
-        return new DerivedSourceStoredFieldsFormat(delegate.storedFieldsFormat(), derivedSourceReadersSupplier, mapperService);
+        return new DerivedSourceStoredFieldsFormat(
+            delegate.storedFieldsFormat(),
+            derivedSourceReadersSupplier,
+            mapperService,
+            delegate.getName()
+        );
     }
 }