diff --git a/output/openapi/elasticsearch-openapi.json b/output/openapi/elasticsearch-openapi.json
index 43ffd4f672..21aaef4c9d 100644
--- a/output/openapi/elasticsearch-openapi.json
+++ b/output/openapi/elasticsearch-openapi.json
@@ -31668,6 +31668,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -31732,6 +31735,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -31801,6 +31807,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -31868,6 +31877,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -121785,6 +121797,16 @@
         },
         "style": "form"
       },
+      "msearch-index_": {
+        "in": "query",
+        "name": "index",
+        "description": "Comma-separated list of data streams, indices, and index aliases to use as default",
+        "deprecated": false,
+        "schema": {
+          "$ref": "#/components/schemas/_types.Indices"
+        },
+        "style": "form"
+      },
       "msearch-max_concurrent_searches": {
         "in": "query",
         "name": "max_concurrent_searches",
diff --git a/output/openapi/elasticsearch-serverless-openapi.json b/output/openapi/elasticsearch-serverless-openapi.json
index e03d8f07a4..c01c8cb5b1 100644
--- a/output/openapi/elasticsearch-serverless-openapi.json
+++ b/output/openapi/elasticsearch-serverless-openapi.json
@@ -19438,6 +19438,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -19502,6 +19505,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -19571,6 +19577,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -19638,6 +19647,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -72817,6 +72829,16 @@
         },
         "style": "form"
       },
+      "msearch-index_": {
+        "in": "query",
+        "name": "index",
+        "description": "Comma-separated list of data streams, indices, and index aliases to use as default",
+        "deprecated": false,
+        "schema": {
+          "$ref": "#/components/schemas/_types.Indices"
+        },
+        "style": "form"
+      },
       "msearch-max_concurrent_searches": {
         "in": "query",
         "name": "max_concurrent_searches",
diff --git a/output/schema/schema.json b/output/schema/schema.json
index 491aebc692..a01195dc83 100644
--- a/output/schema/schema.json
+++ b/output/schema/schema.json
@@ -33038,6 +33038,18 @@
             }
           }
         },
+        {
+          "description": "Comma-separated list of data streams, indices, and index aliases to use as default",
+          "name": "index",
+          "required": false,
+          "type": {
+            "kind": "instance_of",
+            "type": {
+              "name": "Indices",
+              "namespace": "_types"
+            }
+          }
+        },
         {
           "description": "Maximum number of concurrent searches the multi search API can execute.\nDefaults to `max(1, (# of data nodes * min(search thread pool size, 10)))`.",
           "name": "max_concurrent_searches",
@@ -33125,7 +33137,7 @@
           }
         }
       ],
-      "specLocation": "_global/msearch/MultiSearchRequest.ts#L25-L136"
+      "specLocation": "_global/msearch/MultiSearchRequest.ts#L25-L140"
     },
     {
       "kind": "type_alias",
diff --git a/output/schema/validation-errors.json b/output/schema/validation-errors.json
index 859ba73b59..9d31a57f40 100644
--- a/output/schema/validation-errors.json
+++ b/output/schema/validation-errors.json
@@ -13,6 +13,7 @@
         "Request: query parameter 'ignore_throttled' does not exist in the json spec",
         "Request: query parameter 'ignore_unavailable' does not exist in the json spec",
         "Request: query parameter 'include_named_queries_score' does not exist in the json spec",
+        "Request: query parameter 'index' does not exist in the json spec",
         "Request: query parameter 'routing' does not exist in the json spec"
       ],
       "response": []
diff --git a/specification/_global/msearch/MultiSearchRequest.ts b/specification/_global/msearch/MultiSearchRequest.ts
index c448fb7181..4888c0666d 100644
--- a/specification/_global/msearch/MultiSearchRequest.ts
+++ b/specification/_global/msearch/MultiSearchRequest.ts
@@ -99,6 +99,10 @@ export interface Request extends RequestBase {
      * @server_default false
      */
     include_named_queries_score?: boolean
+    /**
+     * Comma-separated list of data streams, indices, and index aliases to use as default
+     */
+    index?: Indices
     /**
      * Maximum number of concurrent searches the multi search API can execute.
      * Defaults to `max(1, (# of data nodes * min(search thread pool size, 10)))`.