diff --git a/temporalio/contrib/google_adk_agents/_plugin.py b/temporalio/contrib/google_adk_agents/_plugin.py
index 03cb78998..9be321398 100644
--- a/temporalio/contrib/google_adk_agents/_plugin.py
+++ b/temporalio/contrib/google_adk_agents/_plugin.py
@@ -10,7 +10,8 @@
 from temporalio.contrib.google_adk_agents._mcp import TemporalMcpToolSetProvider
 from temporalio.contrib.google_adk_agents._model import invoke_model
 from temporalio.contrib.pydantic import (
-    PydanticPayloadConverter as _DefaultPydanticPayloadConverter,
+    PydanticPayloadConverter,
+    ToJsonOptions,
 )
 from temporalio.converter import DataConverter, DefaultPayloadConverter
 from temporalio.plugin import SimplePlugin
@@ -111,11 +112,16 @@ def _configure_data_converter(
         self, converter: DataConverter | None
     ) -> DataConverter:
         if converter is None:
-            return DataConverter(
-                payload_converter_class=_DefaultPydanticPayloadConverter
-            )
+            return DataConverter(payload_converter_class=_AdkPayloadConverter)
         elif converter.payload_converter_class is DefaultPayloadConverter:
             return dataclasses.replace(
-                converter, payload_converter_class=_DefaultPydanticPayloadConverter
+                converter, payload_converter_class=_AdkPayloadConverter
             )
         return converter
+
+
+class _AdkPayloadConverter(PydanticPayloadConverter):
+    """PayloadConverter for Google ADK that strips unset None fields."""
+
+    def __init__(self) -> None:
+        super().__init__(ToJsonOptions(exclude_unset=True))
diff --git a/tests/contrib/google_adk_agents/test_google_adk_agents.py b/tests/contrib/google_adk_agents/test_google_adk_agents.py
index a02e98b3f..e35d58ea6 100644
--- a/tests/contrib/google_adk_agents/test_google_adk_agents.py
+++ b/tests/contrib/google_adk_agents/test_google_adk_agents.py
@@ -14,6 +14,7 @@
 
 """Integration tests for ADK Temporal support."""
 
+import json
 import logging
 import os
 import uuid
@@ -963,3 +964,41 @@ def supported_models(cls) -> list[str]:
     assert result.content is not None
     assert result.content.parts is not None
     assert result.content.parts[0].text == "hello from litellm"
+
+
+def test_unset_none_fields_stripped() -> None:
+    """ADK plugin converter strips unset None fields from Pydantic payloads."""
+    plugin = GoogleAdkPlugin()
+    converter = plugin._configure_data_converter(None)
+    request = LlmRequest(
+        model="gemini-2.0-flash",
+        contents=[Content(parts=[Part(text="hello")])],
+    )
+    payloads = converter.payload_converter.to_payloads([request])
+    serialized = json.loads(payloads[0].data)
+
+    assert serialized["model"] == "gemini-2.0-flash"
+    assert "contents" in serialized
+    for field in (
+        "cache_config",
+        "cache_metadata",
+        "cacheable_contents_token_count",
+        "previous_interaction_id",
+    ):
+        assert field not in serialized, f"Unset field {field!r} should be stripped"
+
+
+def test_explicitly_set_none_preserved() -> None:
+    """Explicitly-set None is preserved (exclude_unset, not exclude_none)."""
+    plugin = GoogleAdkPlugin()
+    converter = plugin._configure_data_converter(None)
+    request = LlmRequest(
+        model="gemini-2.0-flash",
+        contents=[Content(parts=[Part(text="hello")])],
+        cache_config=None,
+    )
+    payloads = converter.payload_converter.to_payloads([request])
+    serialized = json.loads(payloads[0].data)
+
+    assert "cache_config" in serialized, "Explicitly-set None should be preserved"
+    assert serialized["cache_config"] is None