diff --git a/output/openapi/elasticsearch-openapi.json b/output/openapi/elasticsearch-openapi.json
index 8090aa92da..7117ae2685 100644
--- a/output/openapi/elasticsearch-openapi.json
+++ b/output/openapi/elasticsearch-openapi.json
@@ -30879,6 +30879,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -30943,6 +30946,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -31012,6 +31018,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -31079,6 +31088,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -120275,6 +120287,16 @@
         },
         "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": {
+          "$ref": "#/components/schemas/_types.Indices"
+        },
+        "style": "form"
+      },
       "msearch-max_concurrent_searches": {
         "in": "query",
         "name": "max_concurrent_searches",
diff --git a/output/openapi/elasticsearch-serverless-openapi.json b/output/openapi/elasticsearch-serverless-openapi.json
index 805481eecc..eb5adf8854 100644
--- a/output/openapi/elasticsearch-serverless-openapi.json
+++ b/output/openapi/elasticsearch-serverless-openapi.json
@@ -18731,6 +18731,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -18795,6 +18798,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -18864,6 +18870,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -18931,6 +18940,9 @@
           {
             "$ref": "#/components/parameters/msearch-include_named_queries_score"
           },
+          {
+            "$ref": "#/components/parameters/msearch-index_"
+          },
           {
             "$ref": "#/components/parameters/msearch-max_concurrent_searches"
           },
@@ -71578,6 +71590,16 @@
         },
         "style": "form"
       },
+      "msearch-index_": {
+        "in": "query",
+        "name": "index",
+        "description": "Comma-separated list of data streams, indices, and index aliases to use as default",
+        "deprecated": false,
+        "schema": {
+          "$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 8aea7f41a4..ee50c0ed93 100644
--- a/output/schema/schema.json
+++ b/output/schema/schema.json
@@ -32555,6 +32555,18 @@
             }
           }
         },
+        {
+          "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",
@@ -32642,7 +32654,7 @@
           }
         }
       ],
-      "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 310255a5bb..6470f235cb 100644
--- a/output/schema/validation-errors.json
+++ b/output/schema/validation-errors.json
@@ -5,12 +5,6 @@
         "Request: query parameter 'format' does not exist in the json spec"
       ],
       "response": []
-    },
-    "msearch": {
-      "request": [
-        "Request: missing json spec query parameter 'index'"
-      ],
-      "response": []
     }
   },
   "generalErrors": []
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)))`.