Fix #2433: Optimize import time with lazy loading

src/google/adk/__init__.py

@@ -13,11 +13,27 @@
 # limitations under the License.
 
 from __future__ import annotations
+from typing import TYPE_CHECKING
 
-from . import version
-from .agents.context import Context
-from .agents.llm_agent import Agent
-from .runners import Runner
+if TYPE_CHECKING:
+  from .agents.context import Context
+  from .agents.llm_agent import Agent
+  from .runners import Runner
+else:
+  import importlib
+
+  _LAZY_IMPORTS = {
+    "Agent": ".agents.llm_agent",
+    "Context": ".agents.context",
+    "Runner": ".runners",
+  }
 
+  def __getattr__(name: str):
+    if name in _LAZY_IMPORTS:
+      module = importlib.import_module(_LAZY_IMPORTS[name], __name__)
+      return getattr(module, name)
+    raise AttributeError(f"module {__name__} has no attribute {name}")
+
+from . import version
 __version__ = version.__version__
 __all__ = ["Agent", "Context", "Runner"]

src/google/adk/agents/__init__.py

@@ -12,30 +12,57 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from .base_agent import BaseAgent
-from .context import Context
-from .invocation_context import InvocationContext
-from .live_request_queue import LiveRequest
-from .live_request_queue import LiveRequestQueue
-from .llm_agent import Agent
-from .llm_agent import LlmAgent
-from .loop_agent import LoopAgent
-from .mcp_instruction_provider import McpInstructionProvider
-from .parallel_agent import ParallelAgent
-from .run_config import RunConfig
-from .sequential_agent import SequentialAgent
+from __future__ import annotations
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+  from .base_agent import BaseAgent
+  from .context import Context
+  from .invocation_context import InvocationContext
+  from .live_request_queue import LiveRequest
+  from .live_request_queue import LiveRequestQueue
+  from .llm_agent import Agent
+  from .llm_agent import LlmAgent
+  from .loop_agent import LoopAgent
+  from .mcp_instruction_provider import McpInstructionProvider
+  from .parallel_agent import ParallelAgent
+  from .run_config import RunConfig
+  from .sequential_agent import SequentialAgent
+else:
+  import importlib
+
+  _LAZY_IMPORTS = {
+    "Agent": ".llm_agent",
+    "BaseAgent": ".base_agent",
+    "Context": ".context",
+    "InvocationContext": ".invocation_context",
+    "LiveRequest": ".live_request_queue",
+    "LiveRequestQueue": ".live_request_queue",
+    "LlmAgent": ".llm_agent",
+    "LoopAgent": ".loop_agent",
+    "McpInstructionProvider": ".mcp_instruction_provider",
+    "ParallelAgent": ".parallel_agent",
+    "RunConfig": ".run_config",
+    "SequentialAgent": ".sequential_agent",
+  }
+
+  def __getattr__(name: str):
+    if name in _LAZY_IMPORTS:
+      module = importlib.import_module(_LAZY_IMPORTS[name], __name__)
+      return getattr(module, name)
+    raise AttributeError(f"module {__name__} has no attribute {name}")
 
 __all__ = [
-    'Agent',
-    'BaseAgent',
-    'Context',
-    'LlmAgent',
-    'LoopAgent',
-    'McpInstructionProvider',
-    'ParallelAgent',
-    'SequentialAgent',
-    'InvocationContext',
-    'LiveRequest',
-    'LiveRequestQueue',
-    'RunConfig',
+  "Agent",
+  "BaseAgent",
+  "Context",
+  "InvocationContext",
+  "LiveRequest",
+  "LiveRequestQueue",
+  "LlmAgent",
+  "LoopAgent",
+  "McpInstructionProvider",
+  "ParallelAgent",
+  "RunConfig",
+  "SequentialAgent",
 ]

tests/unittests/test_lazy_loading.py

@@ -0,0 +1,28 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import sys
+import unittest
+import google.adk
+
+class TestLazyLoading(unittest.TestCase):
+    def test_agent_not_loaded(self):
+        # Before accessing Agent, it shouldn't be in sys.modules
+        self.assertNotIn("google.adk.agents.llm_agent", sys.modules)
+
+        # Accessing Agent
+        _ = google.adk.Agent
+
+        # Now it should be loaded
+        self.assertIn("google.adk.agents.llm_agent", sys.modules)