diff --git a/specification/grpc/a2a.proto b/specification/grpc/a2a.proto
index 426b84059..faea6c23d 100644
--- a/specification/grpc/a2a.proto
+++ b/specification/grpc/a2a.proto
@@ -172,6 +172,8 @@ message Task {
   // protolint:enable REPEATED_FIELD_NAMES_PLURALIZED
   // A key/value object to store custom metadata about a task.
   google.protobuf.Struct metadata = 6;
+  // Timestamp of the last update to the task, in ISO 8601 format (e.g., "2025-10-28T10:30:00Z").
+  google.protobuf.Timestamp last_updated = 7;
 }
 // --8<-- [end:Task]