Fixed StreamEventData (Azure#43035)

* Fixed StreamEventData

* Resolved comment

Author: howieleung

sdk/ai/azure-ai-agents/CHANGELOG.md

@@ -2,6 +2,14 @@
 
 # Release History
 
+## 1.2.0b5 (Unreleased)
+
+### Features Added
+
+### Bugs Fixed
+- Added `RunStepDeltaChunk` to `StreamEventData` model (GitHub issues [43022](https://github.com/Azure/azure-sdk-for-python/issues/43022))
+
+
 ## 1.2.0b4 (2025-09-12)
 
 ### Features Added

sdk/ai/azure-ai-agents/azure/ai/agents/_version.py

@@ -6,4 +6,4 @@
 # Changes may cause incorrect behavior and will be lost if the code is regenerated.
 # --------------------------------------------------------------------------
 
-VERSION = "1.2.0b4"
+VERSION = "1.2.0b5"

sdk/ai/azure-ai-agents/azure/ai/agents/models/_patch.py

@@ -102,7 +102,7 @@
 
 logger = logging.getLogger(__name__)
 
-StreamEventData = Union["MessageDeltaChunk", "ThreadMessage", ThreadRun, RunStep, str]
+StreamEventData = Union["RunStepDeltaChunk", "MessageDeltaChunk", "ThreadMessage", ThreadRun, RunStep, str]
 
 
 def get_tool_resources(tools: List["Tool"]) -> ToolResources: