diff --git a/openapi/openapiv2.json b/openapi/openapiv2.json
index 1638edc27..8b083a4e9 100644
--- a/openapi/openapiv2.json
+++ b/openapi/openapiv2.json
@@ -7648,6 +7648,17 @@
         }
       }
     },
+    "PayloadExternalPayloadDetails": {
+      "type": "object",
+      "properties": {
+        "sizeBytes": {
+          "type": "string",
+          "format": "int64",
+          "title": "Size in bytes of the externally stored payload"
+        }
+      },
+      "description": "Describes an externally stored object referenced by this payload."
+    },
     "PendingActivityInfoPauseInfo": {
       "type": "object",
       "properties": {
diff --git a/openapi/openapiv3.yaml b/openapi/openapiv3.yaml
index 9f3b310ef..f1374bfc5 100644
--- a/openapi/openapiv3.yaml
+++ b/openapi/openapiv3.yaml
@@ -9823,6 +9823,13 @@ components:
         Represents some binary (byte array) data (ex: activity input parameters or workflow result) with
          metadata which describes this binary data (format, encoding, encryption, etc). Serialization
          of the data may be user-defined.
+    Payload_ExternalPayloadDetails:
+      type: object
+      properties:
+        sizeBytes:
+          type: string
+          description: Size in bytes of the externally stored payload
+      description: Describes an externally stored object referenced by this payload.
     Payloads:
       type: object
       properties:
diff --git a/temporal/api/common/v1/message.proto b/temporal/api/common/v1/message.proto
index 838f5fefc..03b640a2f 100644
--- a/temporal/api/common/v1/message.proto
+++ b/temporal/api/common/v1/message.proto
@@ -32,6 +32,14 @@ message Payloads {
 message Payload {
     map<string,bytes> metadata = 1;
     bytes data = 2;
+    // Details about externally stored payloads associated with this payload.
+    repeated ExternalPayloadDetails external_payloads = 3;
+
+    // Describes an externally stored object referenced by this payload.
+    message ExternalPayloadDetails {
+        // Size in bytes of the externally stored payload
+        int64 size_bytes = 1;
+    }
 }
 
 // A user-defined set of *indexed* fields that are used/exposed when listing/searching workflows.