diff --git a/extras/queue-manager-replicated/core/src/test/java/io/a2a/extras/queuemanager/replicated/core/EventSerializationTest.java b/extras/queue-manager-replicated/core/src/test/java/io/a2a/extras/queuemanager/replicated/core/EventSerializationTest.java
index f05201fb7..7e18ca4a8 100644
--- a/extras/queue-manager-replicated/core/src/test/java/io/a2a/extras/queuemanager/replicated/core/EventSerializationTest.java
+++ b/extras/queue-manager-replicated/core/src/test/java/io/a2a/extras/queuemanager/replicated/core/EventSerializationTest.java
@@ -139,7 +139,7 @@ public void testTaskStatusUpdateEventSerialization() throws JsonProcessingExcept
     public void testTaskArtifactUpdateEventSerialization() throws JsonProcessingException {
         // Create a TaskArtifactUpdateEvent
         List<Part<?>> parts = List.of(new TextPart("Test artifact content"));
-        Artifact artifact = new Artifact("test-artifact-123", "Test Artifact", "Test description", parts, null);
+        Artifact artifact = new Artifact("test-artifact-123", "Test Artifact", "Test description", parts, null, null);
         TaskArtifactUpdateEvent originalEvent = new TaskArtifactUpdateEvent.Builder()
                 .taskId("test-task-xyz")
                 .contextId("test-context-uvw")
diff --git a/server-common/src/main/java/io/a2a/server/util/ArtifactUtils.java b/server-common/src/main/java/io/a2a/server/util/ArtifactUtils.java
index 7a8637680..406113fd4 100644
--- a/server-common/src/main/java/io/a2a/server/util/ArtifactUtils.java
+++ b/server-common/src/main/java/io/a2a/server/util/ArtifactUtils.java
@@ -32,6 +32,7 @@ public static Artifact newArtifact(String name, List<Part<?>> parts, String desc
             name,
             description,
             parts,
+            null,
             null
         );
     }
diff --git a/spec-grpc/src/main/java/io/a2a/grpc/utils/ProtoUtils.java b/spec-grpc/src/main/java/io/a2a/grpc/utils/ProtoUtils.java
index 701947b42..357016054 100644
--- a/spec-grpc/src/main/java/io/a2a/grpc/utils/ProtoUtils.java
+++ b/spec-grpc/src/main/java/io/a2a/grpc/utils/ProtoUtils.java
@@ -875,7 +875,8 @@ public static Message message(io.a2a.grpc.MessageOrBuilder message) {
                     message.getContextId().isEmpty() ? null :  message.getContextId(),
                     message.getTaskId().isEmpty() ? null :  message.getTaskId(),
                     null, // referenceTaskIds is not in grpc message
-                    struct(message.getMetadata())
+                    struct(message.getMetadata()),
+                    message.getExtensionsList().isEmpty() ? null : message.getExtensionsList()
             );
         }
 
@@ -906,7 +907,8 @@ private static Artifact artifact(io.a2a.grpc.ArtifactOrBuilder artifact) {
                     artifact.getName(),
                     artifact.getDescription(),
                     artifact.getPartsList().stream().map(item -> part(item)).collect(Collectors.toList()),
-                    struct(artifact.getMetadata())
+                    struct(artifact.getMetadata()),
+                    artifact.getExtensionsList().isEmpty() ? null : artifact.getExtensionsList()
             );
         }
 
diff --git a/spec/src/main/java/io/a2a/spec/Artifact.java b/spec/src/main/java/io/a2a/spec/Artifact.java
index cb4d1504b..87a48cee4 100644
--- a/spec/src/main/java/io/a2a/spec/Artifact.java
+++ b/spec/src/main/java/io/a2a/spec/Artifact.java
@@ -12,7 +12,8 @@
  */
 @JsonInclude(JsonInclude.Include.NON_ABSENT)
 @JsonIgnoreProperties(ignoreUnknown = true)
-public record Artifact(String artifactId, String name, String description, List<Part<?>> parts, Map<String, Object> metadata) {
+public record Artifact(String artifactId, String name, String description, List<Part<?>> parts, Map<String, Object> metadata,
+                       List<String> extensions) {
 
     public Artifact {
         Assert.checkNotNullParam("artifactId", artifactId);
@@ -28,6 +29,7 @@ public static class Builder {
         private String description;
         private List<Part<?>> parts;
         private Map<String, Object> metadata;
+        private List<String> extensions;
 
         public Builder(){
         }
@@ -38,6 +40,7 @@ public Builder(Artifact existingArtifact) {
             description = existingArtifact.description;
             parts = existingArtifact.parts;
             metadata = existingArtifact.metadata;
+            extensions = existingArtifact.extensions;
         }
 
         public Builder artifactId(String artifactId) {
@@ -71,8 +74,13 @@ public Builder metadata(Map<String, Object> metadata) {
             return this;
         }
 
+        public Builder extensions(List<String> extensions) {
+            this.extensions = this.extensions = (extensions == null) ? null : List.copyOf(extensions);
+            return this;
+        }
+
         public Artifact build() {
-            return new Artifact(artifactId, name, description, parts, metadata);
+            return new Artifact(artifactId, name, description, parts, metadata, extensions);
         }
     }
 }
diff --git a/spec/src/main/java/io/a2a/spec/Message.java b/spec/src/main/java/io/a2a/spec/Message.java
index 8278bec7e..dd7e860a5 100644
--- a/spec/src/main/java/io/a2a/spec/Message.java
+++ b/spec/src/main/java/io/a2a/spec/Message.java
@@ -34,17 +34,18 @@ public final class Message implements EventKind, StreamingEventKind {
     private final Map<String, Object> metadata;
     private final String kind;
     private final List<String> referenceTaskIds;
+    private final List<String> extensions;
 
     public Message(Role role, List<Part<?>> parts, String messageId, String contextId, String taskId,
-                   List<String> referenceTaskIds, Map<String, Object> metadata) {
-        this(role, parts, messageId, contextId, taskId, referenceTaskIds, metadata, MESSAGE);
+                   List<String> referenceTaskIds, Map<String, Object> metadata, List<String> extensions) {
+        this(role, parts, messageId, contextId, taskId, referenceTaskIds, metadata, extensions, MESSAGE);
     }
 
     @JsonCreator
     public Message(@JsonProperty("role") Role role, @JsonProperty("parts") List<Part<?>> parts,
                    @JsonProperty("messageId") String messageId, @JsonProperty("contextId") String contextId,
                    @JsonProperty("taskId") String taskId, @JsonProperty("referenceTaskIds") List<String> referenceTaskIds,
-                   @JsonProperty("metadata") Map<String, Object> metadata,
+                   @JsonProperty("metadata") Map<String, Object> metadata, @JsonProperty("extensions") List<String> extensions,
                    @JsonProperty("kind") String kind) {
         Assert.checkNotNullParam("kind", kind);
         Assert.checkNotNullParam("parts", parts);
@@ -63,6 +64,7 @@ public Message(@JsonProperty("role") Role role, @JsonProperty("parts") List<Part
         this.taskId = taskId;
         this.referenceTaskIds = referenceTaskIds;
         this.metadata = metadata;
+        this.extensions = extensions;
         this.kind = kind;
     }
 
@@ -102,6 +104,10 @@ public List<String> getReferenceTaskIds() {
         return referenceTaskIds;
     }
 
+    public List<String> getExtensions() {
+        return extensions;
+    }
+
     @Override
     public String getKind() {
         return kind;
@@ -132,6 +138,7 @@ public static class Builder {
         private String taskId;
         private List<String> referenceTaskIds;
         private Map<String, Object> metadata;
+        private List<String> extensions;
 
         public Builder() {
         }
@@ -144,6 +151,7 @@ public Builder(Message message) {
             taskId = message.taskId;
             referenceTaskIds = message.referenceTaskIds;
             metadata = message.metadata;
+            extensions = message.extensions;
         }
 
         public Builder role(Role role) {
@@ -186,9 +194,14 @@ public Builder metadata(Map<String, Object> metadata) {
             return this;
         }
 
+        public Builder extensions(List<String> extensions) {
+            this.extensions = (extensions == null) ? null : List.copyOf(extensions);
+            return this;
+        }
+
         public Message build() {
             return new Message(role, parts, messageId == null ? UUID.randomUUID().toString() : messageId,
-                    contextId, taskId, referenceTaskIds, metadata);
+                    contextId, taskId, referenceTaskIds, metadata, extensions);
         }
     }
 }