diff --git a/output/openapi/elasticsearch-openapi.json b/output/openapi/elasticsearch-openapi.json
index 9a323d8456..e3572f75ce 100644
--- a/output/openapi/elasticsearch-openapi.json
+++ b/output/openapi/elasticsearch-openapi.json
@@ -103897,7 +103897,7 @@
                 ]
               },
               "value": {
-                "description": "The value to be appended. Supports template snippets.",
+                "description": "The value to be appended. Supports template snippets. May specify only one of `value` or `copy_from`.",
                 "oneOf": [
                   {
                     "type": "object"
@@ -103910,6 +103910,9 @@
                   }
                 ]
               },
+              "copy_from": {
+                "$ref": "#/components/schemas/_types.Field"
+              },
               "allow_duplicates": {
                 "description": "If `false`, the processor does not append values already present in the field.",
                 "default": true,
@@ -103917,8 +103920,7 @@
               }
             },
             "required": [
-              "field",
-              "value"
+              "field"
             ]
           }
         ]
diff --git a/output/openapi/elasticsearch-serverless-openapi.json b/output/openapi/elasticsearch-serverless-openapi.json
index 44450d2e00..7df14aa15b 100644
--- a/output/openapi/elasticsearch-serverless-openapi.json
+++ b/output/openapi/elasticsearch-serverless-openapi.json
@@ -67856,7 +67856,7 @@
                 ]
               },
               "value": {
-                "description": "The value to be appended. Supports template snippets.",
+                "description": "The value to be appended. Supports template snippets. May specify only one of `value` or `copy_from`.",
                 "oneOf": [
                   {
                     "type": "object"
@@ -67869,6 +67869,9 @@
                   }
                 ]
               },
+              "copy_from": {
+                "$ref": "#/components/schemas/_types.Field"
+              },
               "allow_duplicates": {
                 "description": "If `false`, the processor does not append values already present in the field.",
                 "default": true,
@@ -67876,8 +67879,7 @@
               }
             },
             "required": [
-              "field",
-              "value"
+              "field"
             ]
           }
         ]
diff --git a/output/schema/schema.json b/output/schema/schema.json
index 86a3a245b1..61e7b1c0db 100644
--- a/output/schema/schema.json
+++ b/output/schema/schema.json
@@ -181428,9 +181428,9 @@
           }
         },
         {
-          "description": "The value to be appended. Supports template snippets.",
+          "description": "The value to be appended. Supports template snippets. May specify only one of `value` or `copy_from`.",
           "name": "value",
-          "required": true,
+          "required": false,
           "type": {
             "kind": "union_of",
             "items": [
@@ -181446,6 +181446,18 @@
             ]
           }
         },
+        {
+          "description": "The origin field which will be appended to `field`, cannot set `value` simultaneously.",
+          "name": "copy_from",
+          "required": false,
+          "type": {
+            "kind": "instance_of",
+            "type": {
+              "name": "Field",
+              "namespace": "_types"
+            }
+          }
+        },
         {
           "description": "If `false`, the processor does not append values already present in the field.",
           "name": "allow_duplicates",
@@ -181460,7 +181472,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L329-L344"
+      "specLocation": "ingest/_types/Processors.ts#L329-L348"
     },
     {
       "kind": "interface",
@@ -181580,7 +181592,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L346-L387"
+      "specLocation": "ingest/_types/Processors.ts#L350-L391"
     },
     {
       "kind": "interface",
@@ -181634,7 +181646,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L556-L572"
+      "specLocation": "ingest/_types/Processors.ts#L560-L576"
     },
     {
       "kind": "interface",
@@ -181711,7 +181723,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L574-L597"
+      "specLocation": "ingest/_types/Processors.ts#L578-L601"
     },
     {
       "kind": "interface",
@@ -181870,7 +181882,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L599-L660"
+      "specLocation": "ingest/_types/Processors.ts#L603-L664"
     },
     {
       "kind": "interface",
@@ -181936,7 +181948,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L673-L693"
+      "specLocation": "ingest/_types/Processors.ts#L677-L697"
     },
     {
       "kind": "enum",
@@ -181970,7 +181982,7 @@
         "name": "ConvertType",
         "namespace": "ingest._types"
       },
-      "specLocation": "ingest/_types/Processors.ts#L662-L671"
+      "specLocation": "ingest/_types/Processors.ts#L666-L675"
     },
     {
       "kind": "interface",
@@ -182068,7 +182080,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L695-L728"
+      "specLocation": "ingest/_types/Processors.ts#L699-L732"
     },
     {
       "kind": "interface",
@@ -182293,7 +182305,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L730-L768"
+      "specLocation": "ingest/_types/Processors.ts#L734-L772"
     },
     {
       "kind": "interface",
@@ -182388,7 +182400,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L770-L803"
+      "specLocation": "ingest/_types/Processors.ts#L774-L807"
     },
     {
       "kind": "interface",
@@ -182454,7 +182466,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L805-L824"
+      "specLocation": "ingest/_types/Processors.ts#L809-L828"
     },
     {
       "kind": "interface",
@@ -182689,7 +182701,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L826-L844"
+      "specLocation": "ingest/_types/Processors.ts#L830-L848"
     },
     {
       "kind": "interface",
@@ -182704,7 +182716,7 @@
         "namespace": "ingest._types"
       },
       "properties": [],
-      "specLocation": "ingest/_types/Processors.ts#L846-L846"
+      "specLocation": "ingest/_types/Processors.ts#L850-L850"
     },
     {
       "kind": "interface",
@@ -182808,7 +182820,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L848-L887"
+      "specLocation": "ingest/_types/Processors.ts#L852-L891"
     },
     {
       "kind": "interface",
@@ -182836,7 +182848,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L889-L895"
+      "specLocation": "ingest/_types/Processors.ts#L893-L899"
     },
     {
       "kind": "enum",
@@ -182866,7 +182878,7 @@
         "name": "FingerprintDigest",
         "namespace": "ingest._types"
       },
-      "specLocation": "ingest/_types/Processors.ts#L897-L903"
+      "specLocation": "ingest/_types/Processors.ts#L901-L907"
     },
     {
       "kind": "interface",
@@ -182945,7 +182957,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L905-L933"
+      "specLocation": "ingest/_types/Processors.ts#L909-L937"
     },
     {
       "kind": "interface",
@@ -182998,7 +183010,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L935-L949"
+      "specLocation": "ingest/_types/Processors.ts#L939-L953"
     },
     {
       "kind": "interface",
@@ -183125,7 +183137,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L389-L430"
+      "specLocation": "ingest/_types/Processors.ts#L393-L434"
     },
     {
       "kind": "enum",
@@ -183141,7 +183153,7 @@
         "name": "GeoGridTargetFormat",
         "namespace": "ingest._types"
       },
-      "specLocation": "ingest/_types/Processors.ts#L438-L441"
+      "specLocation": "ingest/_types/Processors.ts#L442-L445"
     },
     {
       "kind": "enum",
@@ -183160,7 +183172,7 @@
         "name": "GeoGridTileType",
         "namespace": "ingest._types"
       },
-      "specLocation": "ingest/_types/Processors.ts#L432-L436"
+      "specLocation": "ingest/_types/Processors.ts#L436-L440"
     },
     {
       "kind": "interface",
@@ -183267,7 +183279,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L443-L477"
+      "specLocation": "ingest/_types/Processors.ts#L447-L481"
     },
     {
       "kind": "interface",
@@ -183372,7 +183384,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L951-L982"
+      "specLocation": "ingest/_types/Processors.ts#L955-L986"
     },
     {
       "kind": "interface",
@@ -183450,7 +183462,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L984-L1008"
+      "specLocation": "ingest/_types/Processors.ts#L988-L1012"
     },
     {
       "kind": "interface",
@@ -183504,7 +183516,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1010-L1026"
+      "specLocation": "ingest/_types/Processors.ts#L1014-L1030"
     },
     {
       "kind": "interface",
@@ -183538,7 +183550,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1067-L1079",
+      "specLocation": "ingest/_types/Processors.ts#L1071-L1083",
       "variants": {
         "kind": "container"
       }
@@ -183615,7 +183627,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1094-L1120"
+      "specLocation": "ingest/_types/Processors.ts#L1098-L1124"
     },
     {
       "kind": "interface",
@@ -183651,7 +183663,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1081-L1092"
+      "specLocation": "ingest/_types/Processors.ts#L1085-L1096"
     },
     {
       "kind": "interface",
@@ -183762,7 +183774,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1028-L1060"
+      "specLocation": "ingest/_types/Processors.ts#L1032-L1064"
     },
     {
       "kind": "interface",
@@ -183843,7 +183855,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1062-L1065"
+      "specLocation": "ingest/_types/Processors.ts#L1066-L1069"
     },
     {
       "kind": "interface",
@@ -183950,7 +183962,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L479-L513"
+      "specLocation": "ingest/_types/Processors.ts#L483-L517"
     },
     {
       "kind": "interface",
@@ -184012,7 +184024,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1122-L1137"
+      "specLocation": "ingest/_types/Processors.ts#L1126-L1141"
     },
     {
       "kind": "interface",
@@ -184091,7 +184103,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1139-L1168"
+      "specLocation": "ingest/_types/Processors.ts#L1143-L1172"
     },
     {
       "kind": "enum",
@@ -184109,7 +184121,7 @@
         "name": "JsonProcessorConflictStrategy",
         "namespace": "ingest._types"
       },
-      "specLocation": "ingest/_types/Processors.ts#L1170-L1175"
+      "specLocation": "ingest/_types/Processors.ts#L1174-L1179"
     },
     {
       "kind": "interface",
@@ -184266,7 +184278,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1177-L1229"
+      "specLocation": "ingest/_types/Processors.ts#L1181-L1233"
     },
     {
       "kind": "interface",
@@ -184341,7 +184353,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1231-L1247"
+      "specLocation": "ingest/_types/Processors.ts#L1235-L1251"
     },
     {
       "kind": "interface",
@@ -184457,7 +184469,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1249-L1283"
+      "specLocation": "ingest/_types/Processors.ts#L1253-L1287"
     },
     {
       "kind": "interface",
@@ -184726,7 +184738,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1285-L1296"
+      "specLocation": "ingest/_types/Processors.ts#L1289-L1300"
     },
     {
       "kind": "interface",
@@ -185709,7 +185721,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1298-L1339"
+      "specLocation": "ingest/_types/Processors.ts#L1302-L1343"
     },
     {
       "kind": "interface",
@@ -185762,7 +185774,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1341-L1357"
+      "specLocation": "ingest/_types/Processors.ts#L1345-L1361"
     },
     {
       "kind": "interface",
@@ -185815,7 +185827,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1359-L1373"
+      "specLocation": "ingest/_types/Processors.ts#L1363-L1377"
     },
     {
       "kind": "interface",
@@ -185868,7 +185880,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1375-L1391"
+      "specLocation": "ingest/_types/Processors.ts#L1379-L1395"
     },
     {
       "kind": "interface",
@@ -185950,7 +185962,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1393-L1421"
+      "specLocation": "ingest/_types/Processors.ts#L1397-L1425"
     },
     {
       "kind": "interface",
@@ -186022,7 +186034,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1423-L1443"
+      "specLocation": "ingest/_types/Processors.ts#L1427-L1447"
     },
     {
       "kind": "interface",
@@ -186108,7 +186120,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1445-L1479"
+      "specLocation": "ingest/_types/Processors.ts#L1449-L1483"
     },
     {
       "kind": "interface",
@@ -186151,7 +186163,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1481-L1490"
+      "specLocation": "ingest/_types/Processors.ts#L1485-L1494"
     },
     {
       "kind": "enum",
@@ -186167,7 +186179,7 @@
         "name": "ShapeType",
         "namespace": "ingest._types"
       },
-      "specLocation": "ingest/_types/Processors.ts#L1492-L1495"
+      "specLocation": "ingest/_types/Processors.ts#L1496-L1499"
     },
     {
       "kind": "interface",
@@ -186266,7 +186278,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1497-L1513"
+      "specLocation": "ingest/_types/Processors.ts#L1501-L1517"
     },
     {
       "kind": "interface",
@@ -186345,7 +186357,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1515-L1540"
+      "specLocation": "ingest/_types/Processors.ts#L1519-L1544"
     },
     {
       "kind": "interface",
@@ -186360,7 +186372,7 @@
         "namespace": "ingest._types"
       },
       "properties": [],
-      "specLocation": "ingest/_types/Processors.ts#L1542-L1542"
+      "specLocation": "ingest/_types/Processors.ts#L1546-L1546"
     },
     {
       "kind": "interface",
@@ -186414,7 +186426,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1544-L1560"
+      "specLocation": "ingest/_types/Processors.ts#L1548-L1564"
     },
     {
       "kind": "interface",
@@ -186468,7 +186480,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1562-L1578"
+      "specLocation": "ingest/_types/Processors.ts#L1566-L1582"
     },
     {
       "kind": "interface",
@@ -186548,7 +186560,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1598-L1624"
+      "specLocation": "ingest/_types/Processors.ts#L1602-L1628"
     },
     {
       "kind": "interface",
@@ -186602,7 +186614,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L1580-L1596"
+      "specLocation": "ingest/_types/Processors.ts#L1584-L1600"
     },
     {
       "kind": "interface",
@@ -186715,7 +186727,7 @@
           }
         }
       ],
-      "specLocation": "ingest/_types/Processors.ts#L515-L546"
+      "specLocation": "ingest/_types/Processors.ts#L519-L550"
     },
     {
       "kind": "enum",
@@ -186740,7 +186752,7 @@
         "name": "UserAgentProperty",
         "namespace": "ingest._types"
       },
-      "specLocation": "ingest/_types/Processors.ts#L548-L554"
+      "specLocation": "ingest/_types/Processors.ts#L552-L558"
     },
     {
       "kind": "interface",
diff --git a/output/typescript/types.ts b/output/typescript/types.ts
index 1bea18a6f8..d22956e3dd 100644
--- a/output/typescript/types.ts
+++ b/output/typescript/types.ts
@@ -14850,7 +14850,8 @@ export type InferenceUpdateResponse = InferenceInferenceEndpointInfo
 
 export interface IngestAppendProcessor extends IngestProcessorBase {
   field: Field
-  value: any | any[]
+  value?: any | any[]
+  copy_from?: Field
   allow_duplicates?: boolean
 }
 
diff --git a/specification/ingest/_types/Processors.ts b/specification/ingest/_types/Processors.ts
index 1455df044a..0b3d08e272 100644
--- a/specification/ingest/_types/Processors.ts
+++ b/specification/ingest/_types/Processors.ts
@@ -333,9 +333,13 @@ export class AppendProcessor extends ProcessorBase {
    */
   field: Field
   /**
-   * The value to be appended. Supports template snippets.
+   * The value to be appended. Supports template snippets. May specify only one of `value` or `copy_from`.
    */
-  value: UserDefinedValue | UserDefinedValue[]
+  value?: UserDefinedValue | UserDefinedValue[]
+  /**
+   * The origin field which will be appended to `field`, cannot set `value` simultaneously.
+   */
+  copy_from?: Field
   /**
    * If `false`, the processor does not append values already present in the field.
    * @server_default true