diff --git a/output/openapi/elasticsearch-openapi.json b/output/openapi/elasticsearch-openapi.json
index a416aedf9f..48f7c3699d 100644
--- a/output/openapi/elasticsearch-openapi.json
+++ b/output/openapi/elasticsearch-openapi.json
@@ -118830,7 +118830,7 @@
             ]
           },
           "username": {
-            "description": "The username to use for authentication with the remote host.",
+            "description": "The username to use for authentication with the remote host (required when using basic auth).",
             "allOf": [
               {
                 "$ref": "#/components/schemas/_types.Username"
@@ -118838,13 +118838,18 @@
             ]
           },
           "password": {
-            "description": "The password to use for authentication with the remote host.",
+            "description": "The password to use for authentication with the remote host (required when using basic auth).",
             "allOf": [
               {
                 "$ref": "#/components/schemas/_types.Password"
               }
             ]
           },
+          "api_key": {
+            "description": "The API key to use for authentication with the remote host (as an alternative to basic auth when the remote cluster is in Elastic Cloud).\n(It is not permitted to set this and also to set an `Authorization` header via `headers`.)",
+            "x-state": "Generally available; Added in 9.3.0",
+            "type": "string"
+          },
           "socket_timeout": {
             "description": "The remote socket read timeout.",
             "default": "30s",
diff --git a/output/openapi/elasticsearch-serverless-openapi.json b/output/openapi/elasticsearch-serverless-openapi.json
index 2431ed80ef..1b81458a00 100644
--- a/output/openapi/elasticsearch-serverless-openapi.json
+++ b/output/openapi/elasticsearch-serverless-openapi.json
@@ -78057,7 +78057,7 @@
             ]
           },
           "username": {
-            "description": "The username to use for authentication with the remote host.",
+            "description": "The username to use for authentication with the remote host (required when using basic auth).",
             "allOf": [
               {
                 "$ref": "#/components/schemas/_types.Username"
@@ -78065,13 +78065,18 @@
             ]
           },
           "password": {
-            "description": "The password to use for authentication with the remote host.",
+            "description": "The password to use for authentication with the remote host (required when using basic auth).",
             "allOf": [
               {
                 "$ref": "#/components/schemas/_types.Password"
               }
             ]
           },
+          "api_key": {
+            "description": "The API key to use for authentication with the remote host (as an alternative to basic auth when the remote cluster is in Elastic Cloud).\n(It is not permitted to set this and also to set an `Authorization` header via `headers`.)",
+            "x-state": "Generally available",
+            "type": "string"
+          },
           "socket_timeout": {
             "description": "The remote socket read timeout.",
             "default": "30s",
diff --git a/output/schema/schema.json b/output/schema/schema.json
index 75a2b0e795..bf940f6671 100644
--- a/output/schema/schema.json
+++ b/output/schema/schema.json
@@ -35969,7 +35969,7 @@
           }
         },
         {
-          "description": "The username to use for authentication with the remote host.",
+          "description": "The username to use for authentication with the remote host (required when using basic auth).",
           "name": "username",
           "required": false,
           "type": {
@@ -35981,7 +35981,7 @@
           }
         },
         {
-          "description": "The password to use for authentication with the remote host.",
+          "description": "The password to use for authentication with the remote host (required when using basic auth).",
           "name": "password",
           "required": false,
           "type": {
@@ -35992,6 +35992,24 @@
             }
           }
         },
+        {
+          "availability": {
+            "serverless": {},
+            "stack": {
+              "since": "9.3.0"
+            }
+          },
+          "description": "The API key to use for authentication with the remote host (as an alternative to basic auth when the remote cluster is in Elastic Cloud).\n(It is not permitted to set this and also to set an `Authorization` header via `headers`.)",
+          "name": "api_key",
+          "required": false,
+          "type": {
+            "kind": "instance_of",
+            "type": {
+              "name": "string",
+              "namespace": "_builtins"
+            }
+          }
+        },
         {
           "description": "The remote socket read timeout.",
           "name": "socket_timeout",
@@ -36006,7 +36024,7 @@
           }
         }
       ],
-      "specLocation": "_global/reindex/types.ts#L112-L140"
+      "specLocation": "_global/reindex/types.ts#L112-L148"
     },
     {
       "kind": "request",
diff --git a/output/typescript/types.ts b/output/typescript/types.ts
index 04b2414291..ae06b8c6fd 100644
--- a/output/typescript/types.ts
+++ b/output/typescript/types.ts
@@ -996,6 +996,7 @@ export interface ReindexRemoteSource {
   host: Host
   username?: Username
   password?: Password
+  api_key?: string
   socket_timeout?: Duration
 }
 
diff --git a/specification/_global/reindex/types.ts b/specification/_global/reindex/types.ts
index af470551b8..133d916a8d 100644
--- a/specification/_global/reindex/types.ts
+++ b/specification/_global/reindex/types.ts
@@ -125,13 +125,21 @@ export class RemoteSource {
    */
   host: Host
   /**
-   * The username to use for authentication with the remote host.
+   * The username to use for authentication with the remote host (required when using basic auth).
    */
   username?: Username
   /**
-   * The password to use for authentication with the remote host.
+   * The password to use for authentication with the remote host (required when using basic auth).
    */
   password?: Password
+  /**
+   * The API key to use for authentication with the remote host (as an alternative to basic auth when the remote cluster is in Elastic Cloud).
+   * (It is not permitted to set this and also to set an `Authorization` header via `headers`.)
+   *
+   * @availability stack since=9.3.0
+   * @availability serverless
+   */
+  api_key?: string
   /**
    * The remote socket read timeout.
    * @server_default 30s