diff --git a/python/packages/core/agent_framework/_types.py b/python/packages/core/agent_framework/_types.py
index a4e3a57330..21a7ce45d7 100644
--- a/python/packages/core/agent_framework/_types.py
+++ b/python/packages/core/agent_framework/_types.py
@@ -2180,7 +2180,16 @@ def value(self) -> ResponseModelT | None:
             and isinstance(self._response_format, type)
             and issubclass(self._response_format, BaseModel)
         ):
-            self._value = cast(ResponseModelT, self._response_format.model_validate_json(self.text))
+            # Concatenate text contents without spaces to preserve structured
+            # output (JSON). Message.text uses " ".join which is correct for
+            # natural language but corrupts JSON keys/values.
+            raw_text = "".join(
+                c.text
+                for msg in self.messages
+                for c in msg.contents
+                if c.type == "text" and c.text is not None
+            )
+            self._value = cast(ResponseModelT, self._response_format.model_validate_json(raw_text))
             self._value_parsed = True
         return self._value
 
@@ -2442,7 +2451,16 @@ def value(self) -> ResponseModelT | None:
             and isinstance(self._response_format, type)
             and issubclass(self._response_format, BaseModel)
         ):
-            self._value = cast(ResponseModelT, self._response_format.model_validate_json(self.text))
+            # Concatenate text contents without spaces to preserve structured
+            # output (JSON). Message.text uses " ".join which is correct for
+            # natural language but corrupts JSON keys/values.
+            raw_text = "".join(
+                c.text
+                for msg in self.messages
+                for c in msg.contents
+                if c.type == "text" and c.text is not None
+            )
+            self._value = cast(ResponseModelT, self._response_format.model_validate_json(raw_text))
             self._value_parsed = True
         return self._value
 
diff --git a/python/packages/core/tests/core/test_types.py b/python/packages/core/tests/core/test_types.py
index 1cde898787..58c2ac26bf 100644
--- a/python/packages/core/tests/core/test_types.py
+++ b/python/packages/core/tests/core/test_types.py
@@ -834,6 +834,51 @@ class StrictSchema(BaseModel):
     assert "score" in error_fields, "Expected 'score' gt constraint error"
 
 
+def test_chat_response_value_multi_chunk_json():
+    """Test that ChatResponse.value correctly parses JSON split across multiple text Content objects.
+
+    When streaming responses arrive as multiple text chunks, Message.text joins
+    them with spaces which corrupts JSON. The value property must concatenate
+    without spaces so model_validate_json succeeds.
+    """
+    # Simulate a JSON response split across multiple text content chunks
+    # (as would happen with streaming)
+    chunks = [
+        Content.from_text(text='{"resp'),
+        Content.from_text(text='onse": "He'),
+        Content.from_text(text='llo"}'),
+    ]
+    message = Message(role="assistant", contents=chunks)
+    response = ChatResponse(messages=message, response_format=OutputModel)
+
+    # Message.text joins with spaces, which would break JSON parsing
+    assert " " in message.text  # confirms the space-join behavior
+
+    # But value should still parse correctly
+    assert response.value is not None
+    assert response.value.response == "Hello"
+
+
+def test_agent_response_value_multi_chunk_json():
+    """Test that AgentResponse.value correctly parses JSON split across multiple text Content objects.
+
+    Same as the ChatResponse test but for AgentResponse, which has its own
+    value property implementation.
+    """
+    chunks = [
+        Content.from_text(text='{"resp'),
+        Content.from_text(text='onse": "He'),
+        Content.from_text(text='llo"}'),
+    ]
+    message = Message(role="assistant", contents=chunks)
+    response = AgentResponse(messages=message, response_format=OutputModel)
+
+    assert " " in message.text  # confirms the space-join behavior
+
+    assert response.value is not None
+    assert response.value.response == "Hello"
+
+
 # region ChatResponseUpdate