diff --git a/packages/gen/gen_ai_hub/orchestration_v2/models/message.py b/packages/gen/gen_ai_hub/orchestration_v2/models/message.py
index eaec35d..d3b40d0 100644
--- a/packages/gen/gen_ai_hub/orchestration_v2/models/message.py
+++ b/packages/gen/gen_ai_hub/orchestration_v2/models/message.py
@@ -164,11 +164,14 @@ class AssistantMessage(BaseModel):
         refusal: A string indicating refusal reason.
 
         tool_calls: A list of tool call objects.
+
+        reasoning_content: A list of reasoning content blocks.
     """
     role: Role = Role.ASSISTANT
     content: Optional[Union[str, List[TextPart]]] = None
     refusal: Optional[str] = None
     tool_calls: Optional[List[MessageToolCall]] = None
+    reasoning_content: Optional[List[ReasoningBlock]] = None
 
 
 class ToolChatMessage(BaseModel):
diff --git a/packages/gen/gen_ai_hub/orchestration_v2/models/response.py b/packages/gen/gen_ai_hub/orchestration_v2/models/response.py
index 91c9f14..59ebcc4 100644
--- a/packages/gen/gen_ai_hub/orchestration_v2/models/response.py
+++ b/packages/gen/gen_ai_hub/orchestration_v2/models/response.py
@@ -6,7 +6,7 @@
 from pydantic import ConfigDict, Field
 
 from gen_ai_hub.orchestration_v2.models.base import ResponseBaseModel
-from gen_ai_hub.orchestration_v2.models.message import ChatMessage, FunctionCall, ResponseChatMessage
+from gen_ai_hub.orchestration_v2.models.message import ChatMessage, FunctionCall, ReasoningBlock, ResponseChatMessage
 
 
 
@@ -189,6 +189,7 @@ class StreamDelta(ResponseBaseModel):
     content: str
     tool_calls: Optional[List[StreamToolCall]] = None
     refusal: Optional[str] = None
+    reasoning_content: Optional[List[ReasoningBlock]] = None
 
 
 class StreamLLMChoice(ResponseBaseModel):
diff --git a/packages/gen/tests/orchestration_v2/test_message_v2.py b/packages/gen/tests/orchestration_v2/test_message_v2.py
index 85ba256..a19ea15 100644
--- a/packages/gen/tests/orchestration_v2/test_message_v2.py
+++ b/packages/gen/tests/orchestration_v2/test_message_v2.py
@@ -1,9 +1,10 @@
 import unittest
 
 from gen_ai_hub.orchestration_v2.models.message import (
-    ReasoningBlock,
+    AssistantMessage,
     FunctionCall,
     MessageToolCall,
+    ReasoningBlock,
     ResponseChatMessage,
 )
 from gen_ai_hub.orchestration_v2.models.response import (
@@ -36,7 +37,7 @@
 
 class TestResponseChatMessageValidation(unittest.TestCase):
 
-    def test_reasoning_content_deserialized_from_dict(self):
+    def test_deserialization_from_dict(self):
         msg = ResponseChatMessage.model_validate({
             "role": "assistant",
             "content": "Hello",
@@ -49,6 +50,20 @@ def test_reasoning_content_optional(self):
         msg = ResponseChatMessage.model_validate({"role": "assistant", "content": "Hello"})
         self.assertIsNone(msg.reasoning_content)
 
+class TestAssistantMessageValidation(unittest.TestCase):
+
+    def test_deserialization_from_dict(self):
+        msg = AssistantMessage.model_validate({
+            "content": "Hello",
+            "reasoning_content": [{"content": "I think...", "signature": "sig123"}],
+        })
+        self.assertIsNotNone(msg.reasoning_content)
+        self.assertIsInstance(msg.reasoning_content[0], ReasoningBlock)
+
+    def test_reasoning_content_optional(self):
+        msg = AssistantMessage.model_validate({"role": "assistant", "content": "Hello"})
+        self.assertIsNone(msg.reasoning_content)
+
 class TestExtraFieldsAllowed(unittest.TestCase):
     """Response-side models (ResponseBaseModel subclasses) must silently accept
     unknown fields so that new API attributes never break existing clients."""
@@ -246,4 +261,4 @@ def test_orchestration_response_with_retries_stores_extra_field(self):
             },
             "extra_field": "extra",
         })
-        self.assertEqual(resp.extra_field, "extra")
\ No newline at end of file
+        self.assertEqual(resp.extra_field, "extra")