feat: Add early exit mechanism to SequentialAgent using escalate action

src/google/adk/agents/sequential_agent.py

@@ -81,7 +81,8 @@ async def _run_async_impl(
           yield event
           if ctx.should_pause_invocation(event):
             pause_invocation = True
-
+          if event.actions and event.actions.escalate:
+            return
       # Skip the rest of the sub-agents if the invocation is paused.
       if pause_invocation:
         return

src/google/adk/tools/exit_sequence_tool.py

@@ -0,0 +1,30 @@
+# Copyright 2025 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.
+
+from .tool_context import ToolContext
+
+
+def exit_sequence(tool_context: ToolContext):
+  """Exits the sequential execution of agents.
+
+  Call this function when you encounter a terminal condition and want to
+  prevent subsequent agents in the sequence from executing. This allows
+  for early termination of a sequential agent workflow when a blocking
+  or final condition is reached.
+
+  Args:
+    tool_context: The context of the current tool invocation.
+  """
+  tool_context.actions.escalate = True
+  tool_context.actions.skip_summarization = True

tests/unittests/agents/test_sequential_agent.py

@@ -22,6 +22,7 @@
 from google.adk.agents.sequential_agent import SequentialAgentState
 from google.adk.apps import ResumabilityConfig
 from google.adk.events.event import Event
+from google.adk.events.event_actions import EventActions
 from google.adk.sessions.in_memory_session_service import InMemorySessionService
 from google.genai import types
 import pytest
@@ -55,6 +56,42 @@ async def _run_live_impl(
     )
 
 
+class _TestingAgentWithEscalateAction(BaseAgent):
+
+  @override
+  async def _run_async_impl(
+      self, ctx: InvocationContext
+  ) -> AsyncGenerator[Event, None]:
+    yield Event(
+        author=self.name,
+        invocation_id=ctx.invocation_id,
+        content=types.Content(
+            parts=[types.Part(text=f'Hello, async {self.name}!')]
+        ),
+        actions=EventActions(escalate=True),
+    )
+    yield Event(
+        author=self.name,
+        invocation_id=ctx.invocation_id,
+        content=types.Content(
+            parts=[types.Part(text=f'I should not be seen after escalation!')]
+        ),
+    )
+
+  @override
+  async def _run_live_impl(
+      self, ctx: InvocationContext
+  ) -> AsyncGenerator[Event, None]:
+    yield Event(
+        author=self.name,
+        invocation_id=ctx.invocation_id,
+        content=types.Content(
+            parts=[types.Part(text=f'Hello, live {self.name}!')]
+        ),
+        actions=EventActions(escalate=True),
+    )
+
+
 async def _create_parent_invocation_context(
     test_name: str, agent: BaseAgent, resumable: bool = False
 ) -> InvocationContext:
@@ -201,3 +238,92 @@ async def test_run_live(request: pytest.FixtureRequest):
   assert events[1].author == agent_2.name
   assert events[0].content.parts[0].text == f'Hello, live {agent_1.name}!'
   assert events[1].content.parts[0].text == f'Hello, live {agent_2.name}!'
+
+
+@pytest.mark.asyncio
+async def test_run_async_with_escalate_action(request: pytest.FixtureRequest):
+  """Test that SequentialAgent exits early when escalate action is triggered."""
+  escalating_agent = _TestingAgentWithEscalateAction(
+      name=f'{request.function.__name__}_escalating_agent'
+  )
+  normal_agent = _TestingAgent(name=f'{request.function.__name__}_normal_agent')
+  sequential_agent = SequentialAgent(
+      name=f'{request.function.__name__}_test_agent',
+      sub_agents=[
+          escalating_agent,
+          normal_agent,  # This should not execute
+      ],
+  )
+  parent_ctx = await _create_parent_invocation_context(
+      request.function.__name__, sequential_agent
+  )
+  events = [e async for e in sequential_agent.run_async(parent_ctx)]
+
+  # Should only have 1 event from the escalating agent, normal agent should not run
+  assert len(events) == 1
+  assert events[0].author == escalating_agent.name
+  assert (
+      events[0].content.parts[0].text
+      == f'Hello, async {escalating_agent.name}!'
+  )
+  assert events[0].actions.escalate is True
+
+
+@pytest.mark.asyncio
+async def test_run_async_escalate_action_in_middle(
+    request: pytest.FixtureRequest,
+):
+  """Test that SequentialAgent exits when escalation happens in middle of sequence."""
+  first_agent = _TestingAgent(name=f'{request.function.__name__}_first_agent')
+  escalating_agent = _TestingAgentWithEscalateAction(
+      name=f'{request.function.__name__}_escalating_agent'
+  )
+  third_agent = _TestingAgent(name=f'{request.function.__name__}_third_agent')
+  sequential_agent = SequentialAgent(
+      name=f'{request.function.__name__}_test_agent',
+      sub_agents=[
+          first_agent,
+          escalating_agent,
+          third_agent,  # This should not execute
+      ],
+  )
+  parent_ctx = await _create_parent_invocation_context(
+      request.function.__name__, sequential_agent
+  )
+  events = [e async for e in sequential_agent.run_async(parent_ctx)]
+
+  # Should have 2 events: one from first agent, one from escalating agent
+  assert len(events) == 2
+  assert events[0].author == first_agent.name
+  assert events[1].author == escalating_agent.name
+  assert events[1].actions.escalate is True
+
+  # Verify third agent did not run
+  third_agent_events = [e for e in events if e.author == third_agent.name]
+  assert len(third_agent_events) == 0
+
+
+@pytest.mark.asyncio
+async def test_run_async_no_escalate_action(request: pytest.FixtureRequest):
+  """Test that SequentialAgent continues normally when no escalate action."""
+  agent_1 = _TestingAgent(name=f'{request.function.__name__}_test_agent_1')
+  agent_2 = _TestingAgent(name=f'{request.function.__name__}_test_agent_2')
+  agent_3 = _TestingAgent(name=f'{request.function.__name__}_test_agent_3')
+  sequential_agent = SequentialAgent(
+      name=f'{request.function.__name__}_test_agent',
+      sub_agents=[
+          agent_1,
+          agent_2,
+          agent_3,
+      ],
+  )
+  parent_ctx = await _create_parent_invocation_context(
+      request.function.__name__, sequential_agent
+  )
+  events = [e async for e in sequential_agent.run_async(parent_ctx)]
+
+  # All agents should execute
+  assert len(events) == 3
+  assert events[0].author == agent_1.name
+  assert events[1].author == agent_2.name
+  assert events[2].author == agent_3.name