diff --git a/server/src/main/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapper.java
index b52bf9759be69..dc8179bab34cf 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapper.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapper.java
@@ -2067,7 +2067,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
             builder.field("type", type);
             builder.field("m", m);
             builder.field("ef_construction", efConstruction);
-            if (confidenceInterval != null) {
+            if (hasSerializableConfidenceInterval(confidenceInterval)) {
                 builder.field("confidence_interval", confidenceInterval);
             }
             if (onDiskRescore) {
@@ -2161,7 +2161,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
             if (rescoreVector != null) {
                 rescoreVector.toXContent(builder, params);
             }
-            if (confidenceInterval != null) {
+            if (hasSerializableConfidenceInterval(confidenceInterval)) {
                 builder.field("confidence_interval", confidenceInterval);
             }
             builder.endObject();
@@ -3555,6 +3555,10 @@ private static Float parseConfidenceInterval(String fieldName, Map<String, ?> in
         return confidenceInterval;
     }
 
+    private static boolean hasSerializableConfidenceInterval(Float confidenceInterval) {
+        return confidenceInterval != null && Float.compare(confidenceInterval, 0.0f) != 0;
+    }
+
     /**
      * @return the custom kNN vectors format that is configured for this field or
      * {@code null} if the default format should be used.
diff --git a/server/src/test/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapperTests.java b/server/src/test/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapperTests.java
index a956441219ada..685fd546ca2a9 100644
--- a/server/src/test/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapperTests.java
+++ b/server/src/test/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapperTests.java
@@ -85,6 +85,7 @@
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.hasToString;
 import static org.hamcrest.Matchers.instanceOf;
+import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.startsWith;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
@@ -2033,6 +2034,41 @@ public void testConfidenceIntervalNoDeprecationBeforeLatestIndexVersion() throws
         assertWarnings();
     }
 
+    public void testConfidenceIntervalZeroNormalizedAndOmittedFromMappingSource() throws IOException {
+        DocumentMapper mapper = createDocumentMapper(IndexVersions.UPGRADE_TO_LUCENE_10_4_0, fieldMapping(b -> {
+            b.field("type", "dense_vector");
+            b.field("dims", 6);
+            b.field("index", true);
+            b.field("similarity", "dot_product");
+            b.startObject("index_options");
+            b.field("type", "int4_hnsw");
+            b.field("m", 16);
+            b.field("ef_construction", 100);
+            b.field("confidence_interval", 0.0);
+            b.endObject();
+        }));
+        String source = mapper.mappingSource().string();
+        assertThat(source, containsString("\"type\":\"int4_hnsw\""));
+        assertThat(source, not(containsString("confidence_interval")));
+    }
+
+    public void testConfidenceIntervalAbsentInt4HnswMappingSourceStable() throws IOException {
+        DocumentMapper mapper = createDocumentMapper(IndexVersions.UPGRADE_TO_LUCENE_10_4_0, fieldMapping(b -> {
+            b.field("type", "dense_vector");
+            b.field("dims", 6);
+            b.field("index", true);
+            b.field("similarity", "dot_product");
+            b.startObject("index_options");
+            b.field("type", "int4_hnsw");
+            b.field("m", 16);
+            b.field("ef_construction", 100);
+            b.endObject();
+        }));
+        String source = mapper.mappingSource().string();
+        assertThat(source, containsString("\"type\":\"int4_hnsw\""));
+        assertThat(source, not(containsString("confidence_interval")));
+    }
+
     public void testKnnQuantizedFlatVectorsFormat() throws IOException {
         for (String quantizedFlatFormat : new String[] { "int8_flat", "int4_flat" }) {
             MapperService mapperService = createMapperService(