diff --git a/src/google/adk/tools/base_toolset.py b/src/google/adk/tools/base_toolset.py
index 25f0d6a2a2..e3f16a145e 100644
--- a/src/google/adk/tools/base_toolset.py
+++ b/src/google/adk/tools/base_toolset.py
@@ -17,6 +17,7 @@
 from abc import ABC
 from abc import abstractmethod
 import copy
+from typing import Callable
 from typing import final
 from typing import List
 from typing import Optional
@@ -27,6 +28,8 @@
 from typing import TypeVar
 from typing import Union
 
+from google.genai import types
+
 from ..agents.readonly_context import ReadonlyContext
 from ..auth.auth_tool import AuthConfig
 from .base_tool import BaseTool
@@ -80,8 +83,7 @@ def __init__(
     """
     self.tool_filter = tool_filter
     self.tool_name_prefix = tool_name_prefix
-    self._cached_invocation_id: Optional[str] = None
-    self._cached_prefixed_tools: Optional[list[BaseTool]] = None
+    self._cached_prefixed_tools: dict[Optional[str], list[BaseTool]] = {}
     self._use_invocation_cache = True
 
   @abstractmethod
@@ -119,16 +121,14 @@ async def get_tools_with_prefix(
 
     if (
         self._use_invocation_cache
-        and self._cached_prefixed_tools is not None
-        and self._cached_invocation_id == invocation_id
+        and invocation_id in self._cached_prefixed_tools
     ):
-      return self._cached_prefixed_tools
+      return self._cached_prefixed_tools[invocation_id]
 
     tools = await self.get_tools(readonly_context)
 
     if not self.tool_name_prefix:
-      self._cached_invocation_id = invocation_id
-      self._cached_prefixed_tools = tools
+      self._cached_prefixed_tools[invocation_id] = tools
       return tools
 
     prefix = self.tool_name_prefix
@@ -146,10 +146,12 @@ async def get_tools_with_prefix(
       # Also update the function declaration name if the tool has one
       # Use default parameters to capture the current values in the closure
       def _create_prefixed_declaration(
-          original_get_declaration=tool._get_declaration,
-          prefixed_name=prefixed_name,
-      ):
-        def _get_prefixed_declaration():
+          original_get_declaration: Callable[
+              [], Optional[types.FunctionDeclaration]
+          ] = tool._get_declaration,
+          prefixed_name: str = prefixed_name,
+      ) -> Callable[[], Optional[types.FunctionDeclaration]]:
+        def _get_prefixed_declaration() -> Optional[types.FunctionDeclaration]:
           declaration = original_get_declaration()
           if declaration is not None:
             declaration.name = prefixed_name
@@ -161,8 +163,7 @@ def _get_prefixed_declaration():
       tool_copy._get_declaration = _create_prefixed_declaration()
       prefixed_tools.append(tool_copy)
 
-    self._cached_invocation_id = invocation_id
-    self._cached_prefixed_tools = prefixed_tools
+    self._cached_prefixed_tools[invocation_id] = prefixed_tools
     return prefixed_tools
 
   async def close(self) -> None:
@@ -174,6 +175,7 @@ async def close(self) -> None:
       should ensure that any open connections, files, or other managed
       resources are properly released to prevent leaks.
     """
+    self._cached_prefixed_tools.clear()
 
   @classmethod
   def from_config(
diff --git a/tests/unittests/tools/test_base_toolset.py b/tests/unittests/tools/test_base_toolset.py
index cdb7808db7..a6a97cc33a 100644
--- a/tests/unittests/tools/test_base_toolset.py
+++ b/tests/unittests/tools/test_base_toolset.py
@@ -41,14 +41,16 @@ class _TestingToolset(BaseToolset):
   def __init__(self, *args, tools: Optional[list[BaseTool]] = None, **kwargs):
     super().__init__(*args, **kwargs)
     self._tools = tools or []
+    self.get_tools_call_count = 0
 
   async def get_tools(
       self, readonly_context: Optional[ReadonlyContext] = None
   ) -> list[BaseTool]:
+    self.get_tools_call_count += 1
     return self._tools
 
   async def close(self) -> None:
-    pass
+    await super().close()
 
 
 @pytest.mark.asyncio
@@ -439,6 +441,14 @@ async def test_get_tools_with_prefix_caching():
   assert tools3 is not tools1  # Should be a new list instance
   assert tools3[0].name == 'test_tool1'
 
+  # The first invocation should still be cached after another invocation uses
+  # the same toolset.
+  tools1_again = await toolset.get_tools_with_prefix(
+      readonly_context=readonly_context1
+  )
+  assert tools1_again is tools1
+  assert toolset.get_tools_call_count == 2
+
   # Test disabling caching
   toolset._use_invocation_cache = False
   tools4 = await toolset.get_tools_with_prefix(
@@ -448,3 +458,16 @@ async def test_get_tools_with_prefix_caching():
       readonly_context=readonly_context2
   )
   assert tools4 is not tools5
+
+
+@pytest.mark.asyncio
+async def test_get_tools_with_prefix_close_clears_cache():
+  tool1 = _TestingTool(name='tool1', description='Test tool 1')
+  toolset = _TestingToolset(tools=[tool1], tool_name_prefix='test')
+
+  await toolset.get_tools_with_prefix()
+  assert toolset._cached_prefixed_tools
+
+  await toolset.close()
+
+  assert not toolset._cached_prefixed_tools