diff --git a/output/openapi/elasticsearch-serverless-openapi.json b/output/openapi/elasticsearch-serverless-openapi.json
index af4ab7ab46..9f8c94e886 100644
--- a/output/openapi/elasticsearch-serverless-openapi.json
+++ b/output/openapi/elasticsearch-serverless-openapi.json
@@ -10027,6 +10027,9 @@
                     "items": {
                       "type": "string"
                     }
+                  },
+                  "prefix_strings": {
+                    "$ref": "#/components/schemas/ml._types:TrainedModelPrefixStrings"
                   }
                 }
               }
@@ -54361,11 +54364,7 @@
             "description": "String prepended to input at search",
             "type": "string"
           }
-        },
-        "required": [
-          "ingest",
-          "search"
-        ]
+        }
       },
       "ml._types:TrainedModelStats": {
         "type": "object",
diff --git a/output/schema/schema.json b/output/schema/schema.json
index a42d8a8c9a..44eb0ff7fd 100644
--- a/output/schema/schema.json
+++ b/output/schema/schema.json
@@ -146444,7 +146444,7 @@
         {
           "description": "String prepended to input at ingest",
           "name": "ingest",
-          "required": true,
+          "required": false,
           "type": {
             "kind": "instance_of",
             "type": {
@@ -146456,7 +146456,7 @@
         {
           "description": "String prepended to input at search",
           "name": "search",
-          "required": true,
+          "required": false,
           "type": {
             "kind": "instance_of",
             "type": {
@@ -155894,6 +155894,27 @@
                 }
               }
             }
+          },
+          {
+            "availability": {
+              "serverless": {
+                "since": "8.12.0"
+              },
+              "stack": {
+                "since": "8.12.0"
+              }
+            },
+            "description": "Optional prefix strings applied at inference",
+            "name": "prefix_strings",
+            "required": false,
+            "since": "8.12.0",
+            "type": {
+              "kind": "instance_of",
+              "type": {
+                "name": "TrainedModelPrefixStrings",
+                "namespace": "ml._types"
+              }
+            }
           }
         ]
       },
@@ -155944,7 +155965,7 @@
           }
         }
       ],
-      "specLocation": "ml/put_trained_model/MlPutTrainedModelRequest.ts#L28-L106"
+      "specLocation": "ml/put_trained_model/MlPutTrainedModelRequest.ts#L29-L113"
     },
     {
       "body": {
diff --git a/output/typescript/types.ts b/output/typescript/types.ts
index 8e5e073657..dd4728d8e4 100644
--- a/output/typescript/types.ts
+++ b/output/typescript/types.ts
@@ -13391,8 +13391,8 @@ export interface MlTrainedModelLocationIndex {
 }
 
 export interface MlTrainedModelPrefixStrings {
-  ingest: string
-  search: string
+  ingest?: string
+  search?: string
 }
 
 export interface MlTrainedModelSizeStats {
@@ -14415,6 +14415,7 @@ export interface MlPutTrainedModelRequest extends RequestBase {
     model_size_bytes?: long
     platform_architecture?: string
     tags?: string[]
+    prefix_strings?: MlTrainedModelPrefixStrings
   }
 }
 
diff --git a/specification/ml/_types/TrainedModel.ts b/specification/ml/_types/TrainedModel.ts
index acd5c0c64e..c55b106b5f 100644
--- a/specification/ml/_types/TrainedModel.ts
+++ b/specification/ml/_types/TrainedModel.ts
@@ -429,9 +429,9 @@ export class TrainedModelPrefixStrings {
   /**
    * String prepended to input at ingest
    */
-  ingest: string
+  ingest?: string
   /**
    * String prepended to input at search
    */
-  search: string
+  search?: string
 }
diff --git a/specification/ml/put_trained_model/MlPutTrainedModelRequest.ts b/specification/ml/put_trained_model/MlPutTrainedModelRequest.ts
index 4c5b5d0b7d..4cb40ca309 100644
--- a/specification/ml/put_trained_model/MlPutTrainedModelRequest.ts
+++ b/specification/ml/put_trained_model/MlPutTrainedModelRequest.ts
@@ -22,6 +22,7 @@ import { RequestBase } from '@_types/Base'
 import { Id } from '@_types/common'
 import { long } from '@_types/Numeric'
 import { Definition, Input } from './types'
+import { TrainedModelPrefixStrings } from '../_types/TrainedModel'
 import { TrainedModelType } from '../_types/TrainedModel'
 import { InferenceConfigCreateContainer } from '@ml/_types/inference'
 
@@ -102,5 +103,11 @@ export interface Request extends RequestBase {
      * An array of tags to organize the model.
      */
     tags?: string[]
+    /**
+     * Optional prefix strings applied at inference
+     * @availability stack since=8.12.0
+     * @availability serverless
+     */
+    prefix_strings?: TrainedModelPrefixStrings
   }
 }