From b08e2a1d7e77565b49db712d2ffc520cde548fbd Mon Sep 17 00:00:00 2001
From: Kathleen DeRusso <kathleen.derusso@elastic.co>
Date: Mon, 16 Jun 2025 14:51:11 -0400
Subject: [PATCH] Include default index option type to defaults

---
 .../common/settings/IndexScopedSettings.java          |  1 +
 .../index/mapper/InferenceMetadataFieldsMapper.java   | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java b/server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java
index 0ff64f14dc17..5d778bea93fa 100644
--- a/server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java
+++ b/server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java
@@ -203,6 +203,7 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
                 IndexSettings.INDEX_MAPPER_SOURCE_MODE_SETTING,
                 IndexSettings.RECOVERY_USE_SYNTHETIC_SOURCE_SETTING,
                 InferenceMetadataFieldsMapper.USE_LEGACY_SEMANTIC_TEXT_FORMAT,
+                InferenceMetadataFieldsMapper.DEFAULT_SEMANTIC_TEXT_INDEX_OPTIONS,
 
                 // validate that built-in similarities don't get redefined
                 Setting.groupSetting("index.similarity.", (s) -> {
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/InferenceMetadataFieldsMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/InferenceMetadataFieldsMapper.java
index 2dcd92be0952..0dc34f5d9c38 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/InferenceMetadataFieldsMapper.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/InferenceMetadataFieldsMapper.java
@@ -17,11 +17,14 @@ import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.index.IndexVersion;
 import org.elasticsearch.index.IndexVersions;
+import org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper;
 import org.elasticsearch.index.query.SearchExecutionContext;
 
 import java.util.Map;
 import java.util.function.Function;
 
+import static org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper.VectorIndexType.BBQ_HNSW;
+
 /**
  * An abstract {@link MetadataFieldMapper} used as a placeholder for implementation
  * in the inference module. It is required by {@link SourceFieldMapper} to identify
@@ -42,6 +45,14 @@ public abstract class InferenceMetadataFieldsMapper extends MetadataFieldMapper
         Setting.Property.InternalIndex
     );
 
+    public static final Setting<String> DEFAULT_SEMANTIC_TEXT_INDEX_OPTIONS = Setting.simpleString(
+        "index.mapping.semantic_text.default_index_options_type",
+        BBQ_HNSW.getName(),
+        Setting.Property.Final,
+        Setting.Property.IndexScope,
+        Setting.Property.InternalIndex
+    );
+
     // Check index version SOURCE_MAPPER_MODE_ATTRIBUTE_NOOP because that index version was added in the same serverless promotion
     // where the new format was enabled by default
     public static final IndexVersion USE_NEW_SEMANTIC_TEXT_FORMAT_BY_DEFAULT = IndexVersions.SOURCE_MAPPER_MODE_ATTRIBUTE_NOOP;