Mark hooks as non-experimental (strands-agents#410)

We've keep model & tool events as experimental but *Invocation and Message events are now marked as 'stable'

Author: zastrowm

src/strands/agent/agent.py

@@ -20,14 +20,15 @@
 from pydantic import BaseModel
 
 from ..event_loop.event_loop import event_loop_cycle, run_tool
-from ..experimental.hooks import (
+from ..handlers.callback_handler import PrintingCallbackHandler, null_callback_handler
+from ..hooks import (
     AfterInvocationEvent,
     AgentInitializedEvent,
     BeforeInvocationEvent,
+    HookProvider,
     HookRegistry,
     MessageAddedEvent,
 )
-from ..handlers.callback_handler import PrintingCallbackHandler, null_callback_handler
 from ..models.bedrock import BedrockModel
 from ..telemetry.metrics import EventLoopMetrics
 from ..telemetry.tracer import get_tracer
@@ -202,6 +203,7 @@ def __init__(
         name: Optional[str] = None,
         description: Optional[str] = None,
         state: Optional[Union[AgentState, dict]] = None,
+        hooks: Optional[list[HookProvider]] = None,
     ):
         """Initialize the Agent with the specified configuration.
 
@@ -238,6 +240,8 @@ def __init__(
                 Defaults to None.
             state: stateful information for the agent. Can be either an AgentState object, or a json serializable dict.
                 Defaults to an empty AgentState object.
+            hooks: hooks to be added to the agent hook registry
+                Defaults to None.
         """
         self.model = BedrockModel() if not model else BedrockModel(model_id=model) if isinstance(model, str) else model
         self.messages = messages if messages is not None else []
@@ -301,9 +305,11 @@ def __init__(
         self.name = name or _DEFAULT_AGENT_NAME
         self.description = description
 
-        self._hooks = HookRegistry()
-        # Register built-in hook providers (like ConversationManager) here
-        self._hooks.invoke_callbacks(AgentInitializedEvent(agent=self))
+        self.hooks = HookRegistry()
+        if hooks:
+            for hook in hooks:
+                self.hooks.add_hook(hook)
+        self.hooks.invoke_callbacks(AgentInitializedEvent(agent=self))
 
     @property
     def tool(self) -> ToolCaller:
@@ -424,7 +430,7 @@ async def structured_output_async(
         Raises:
             ValueError: If no conversation history or prompt is provided.
         """
-        self._hooks.invoke_callbacks(BeforeInvocationEvent(agent=self))
+        self.hooks.invoke_callbacks(BeforeInvocationEvent(agent=self))
 
         try:
             if not self.messages and not prompt:
@@ -443,7 +449,7 @@ async def structured_output_async(
             return event["output"]
 
         finally:
-            self._hooks.invoke_callbacks(AfterInvocationEvent(agent=self))
+            self.hooks.invoke_callbacks(AfterInvocationEvent(agent=self))
 
     async def stream_async(self, prompt: Union[str, list[ContentBlock]], **kwargs: Any) -> AsyncIterator[Any]:
         """Process a natural language prompt and yield events as an async iterator.
@@ -509,7 +515,7 @@ async def _run_loop(self, message: Message, kwargs: dict[str, Any]) -> AsyncGene
         Yields:
             Events from the event loop cycle.
         """
-        self._hooks.invoke_callbacks(BeforeInvocationEvent(agent=self))
+        self.hooks.invoke_callbacks(BeforeInvocationEvent(agent=self))
 
         try:
             yield {"callback": {"init_event_loop": True, **kwargs}}
@@ -523,7 +529,7 @@ async def _run_loop(self, message: Message, kwargs: dict[str, Any]) -> AsyncGene
 
         finally:
             self.conversation_manager.apply_management(self)
-            self._hooks.invoke_callbacks(AfterInvocationEvent(agent=self))
+            self.hooks.invoke_callbacks(AfterInvocationEvent(agent=self))
 
     async def _execute_event_loop_cycle(self, kwargs: dict[str, Any]) -> AsyncGenerator[dict[str, Any], None]:
         """Execute the event loop cycle with retry logic for context window limits.
@@ -653,4 +659,4 @@ def _end_agent_trace_span(
     def _append_message(self, message: Message) -> None:
         """Appends a message to the agent's list of messages and invokes the callbacks for the MessageCreatedEvent."""
         self.messages.append(message)
-        self._hooks.invoke_callbacks(MessageAddedEvent(agent=self, message=message))
+        self.hooks.invoke_callbacks(MessageAddedEvent(agent=self, message=message))

src/strands/event_loop/event_loop.py

@@ -18,8 +18,9 @@
     AfterToolInvocationEvent,
     BeforeModelInvocationEvent,
     BeforeToolInvocationEvent,
+)
+from ..hooks import (
     MessageAddedEvent,
-    get_registry,
 )
 from ..telemetry.metrics import Trace
 from ..telemetry.tracer import get_tracer
@@ -120,7 +121,7 @@ async def event_loop_cycle(agent: "Agent", kwargs: dict[str, Any]) -> AsyncGener
 
         tool_specs = agent.tool_registry.get_all_tool_specs()
 
-        get_registry(agent).invoke_callbacks(
+        agent.hooks.invoke_callbacks(
             BeforeModelInvocationEvent(
                 agent=agent,
             )
@@ -136,7 +137,7 @@ async def event_loop_cycle(agent: "Agent", kwargs: dict[str, Any]) -> AsyncGener
             stop_reason, message, usage, metrics = event["stop"]
             kwargs.setdefault("request_state", {})
 
-            get_registry(agent).invoke_callbacks(
+            agent.hooks.invoke_callbacks(
                 AfterModelInvocationEvent(
                     agent=agent,
                     stop_response=AfterModelInvocationEvent.ModelStopResponse(
@@ -154,7 +155,7 @@ async def event_loop_cycle(agent: "Agent", kwargs: dict[str, Any]) -> AsyncGener
             if model_invoke_span:
                 tracer.end_span_with_error(model_invoke_span, str(e), e)
 
-            get_registry(agent).invoke_callbacks(
+            agent.hooks.invoke_callbacks(
                 AfterModelInvocationEvent(
                     agent=agent,
                     exception=e,
@@ -188,7 +189,7 @@ async def event_loop_cycle(agent: "Agent", kwargs: dict[str, Any]) -> AsyncGener
 
         # Add the response message to the conversation
         agent.messages.append(message)
-        get_registry(agent).invoke_callbacks(MessageAddedEvent(agent=agent, message=message))
+        agent.hooks.invoke_callbacks(MessageAddedEvent(agent=agent, message=message))
         yield {"callback": {"message": message}}
 
         # Update metrics
@@ -308,7 +309,7 @@ async def run_tool(agent: "Agent", tool_use: ToolUse, kwargs: dict[str, Any]) ->
         }
     )
 
-    before_event = get_registry(agent).invoke_callbacks(
+    before_event = agent.hooks.invoke_callbacks(
         BeforeToolInvocationEvent(
             agent=agent,
             selected_tool=tool_func,
@@ -342,7 +343,7 @@ async def run_tool(agent: "Agent", tool_use: ToolUse, kwargs: dict[str, Any]) ->
                 "content": [{"text": f"Unknown tool: {tool_name}"}],
             }
             # for every Before event call, we need to have an AfterEvent call
-            after_event = get_registry(agent).invoke_callbacks(
+            after_event = agent.hooks.invoke_callbacks(
                 AfterToolInvocationEvent(
                     agent=agent,
                     selected_tool=selected_tool,
@@ -359,7 +360,7 @@ async def run_tool(agent: "Agent", tool_use: ToolUse, kwargs: dict[str, Any]) ->
 
         result = event
 
-        after_event = get_registry(agent).invoke_callbacks(
+        after_event = agent.hooks.invoke_callbacks(
             AfterToolInvocationEvent(
                 agent=agent,
                 selected_tool=selected_tool,
@@ -377,7 +378,7 @@ async def run_tool(agent: "Agent", tool_use: ToolUse, kwargs: dict[str, Any]) ->
             "status": "error",
             "content": [{"text": f"Error: {str(e)}"}],
         }
-        after_event = get_registry(agent).invoke_callbacks(
+        after_event = agent.hooks.invoke_callbacks(
             AfterToolInvocationEvent(
                 agent=agent,
                 selected_tool=selected_tool,
@@ -454,7 +455,7 @@ def tool_handler(tool_use: ToolUse) -> ToolGenerator:
     }
 
     agent.messages.append(tool_result_message)
-    get_registry(agent).invoke_callbacks(MessageAddedEvent(agent=agent, message=tool_result_message))
+    agent.hooks.invoke_callbacks(MessageAddedEvent(agent=agent, message=tool_result_message))
     yield {"callback": {"message": tool_result_message}}
 
     if cycle_span:

src/strands/experimental/hooks/__init__.py

@@ -1,58 +1,15 @@
-"""Typed hook system for extending agent functionality.
-
-This module provides a composable mechanism for building objects that can hook
-into specific events during the agent lifecycle. The hook system enables both
-built-in SDK components and user code to react to or modify agent behavior
-through strongly-typed event callbacks.
-
-Example Usage:
-    ```python
-    from strands.hooks import HookProvider, HookRegistry
-    from strands.hooks.events import StartRequestEvent, EndRequestEvent
-
-    class LoggingHooks(HookProvider):
-        def register_hooks(self, registry: HookRegistry) -> None:
-            registry.add_callback(StartRequestEvent, self.log_start)
-            registry.add_callback(EndRequestEvent, self.log_end)
-
-        def log_start(self, event: StartRequestEvent) -> None:
-            print(f"Request started for {event.agent.name}")
-
-        def log_end(self, event: EndRequestEvent) -> None:
-            print(f"Request completed for {event.agent.name}")
-
-    # Use with agent
-    agent = Agent(hooks=[LoggingHooks()])
-    ```
-
-This replaces the older callback_handler approach with a more composable,
-type-safe system that supports multiple subscribers per event type.
-"""
+"""Experimental hook functionality that has not yet reached stability."""
 
 from .events import (
-    AfterInvocationEvent,
     AfterModelInvocationEvent,
     AfterToolInvocationEvent,
-    AgentInitializedEvent,
-    BeforeInvocationEvent,
     BeforeModelInvocationEvent,
     BeforeToolInvocationEvent,
-    MessageAddedEvent,
 )
-from .registry import HookCallback, HookEvent, HookProvider, HookRegistry, get_registry
 
 __all__ = [
-    "AgentInitializedEvent",
-    "BeforeInvocationEvent",
-    "AfterInvocationEvent",
-    "BeforeModelInvocationEvent",
-    "AfterModelInvocationEvent",
     "BeforeToolInvocationEvent",
     "AfterToolInvocationEvent",
-    "MessageAddedEvent",
-    "HookEvent",
-    "HookProvider",
-    "HookCallback",
-    "HookRegistry",
-    "get_registry",
+    "BeforeModelInvocationEvent",
+    "AfterModelInvocationEvent",
 ]

src/strands/experimental/hooks/events.py

@@ -1,67 +1,15 @@
-"""Hook events emitted as part of invoking Agents.
+"""Experimental hook events emitted as part of invoking Agents.
 
 This module defines the events that are emitted as Agents run through the lifecycle of a request.
 """
 
 from dataclasses import dataclass
 from typing import Any, Optional
 
+from ...hooks import HookEvent
 from ...types.content import Message
 from ...types.streaming import StopReason
 from ...types.tools import AgentTool, ToolResult, ToolUse
-from .registry import HookEvent
-
-
-@dataclass
-class AgentInitializedEvent(HookEvent):
-    """Event triggered when an agent has finished initialization.
-
-    This event is fired after the agent has been fully constructed and all
-    built-in components have been initialized. Hook providers can use this
-    event to perform setup tasks that require a fully initialized agent.
-    """
-
-    pass
-
-
-@dataclass
-class BeforeInvocationEvent(HookEvent):
-    """Event triggered at the beginning of a new agent request.
-
-    This event is fired before the agent begins processing a new user request,
-    before any model inference or tool execution occurs. Hook providers can
-    use this event to perform request-level setup, logging, or validation.
-
-    This event is triggered at the beginning of the following api calls:
-      - Agent.__call__
-      - Agent.stream_async
-      - Agent.structured_output
-    """
-
-    pass
-
-
-@dataclass
-class AfterInvocationEvent(HookEvent):
-    """Event triggered at the end of an agent request.
-
-    This event is fired after the agent has completed processing a request,
-    regardless of whether it completed successfully or encountered an error.
-    Hook providers can use this event for cleanup, logging, or state persistence.
-
-    Note: This event uses reverse callback ordering, meaning callbacks registered
-    later will be invoked first during cleanup.
-
-    This event is triggered at the end of the following api calls:
-      - Agent.__call__
-      - Agent.stream_async
-      - Agent.structured_output
-    """
-
-    @property
-    def should_reverse_callbacks(self) -> bool:
-        """True to invoke callbacks in reverse order."""
-        return True
 
 
 @dataclass
@@ -173,22 +121,3 @@ class ModelStopResponse:
     def should_reverse_callbacks(self) -> bool:
         """True to invoke callbacks in reverse order."""
         return True
-
-
-@dataclass
-class MessageAddedEvent(HookEvent):
-    """Event triggered when a message is added to the agent's conversation.
-
-    This event is fired whenever the agent adds a new message to its internal
-    message history, including user messages, assistant responses, and tool
-    results. Hook providers can use this event for logging, monitoring, or
-    implementing custom message processing logic.
-
-    Note: This event is only triggered for messages added by the framework
-    itself, not for messages manually added by tools or external code.
-
-    Attributes:
-        message: The message that was added to the conversation history.
-    """
-
-    message: Message

src/strands/hooks/__init__.py

@@ -0,0 +1,49 @@
+"""Typed hook system for extending agent functionality.
+
+This module provides a composable mechanism for building objects that can hook
+into specific events during the agent lifecycle. The hook system enables both
+built-in SDK components and user code to react to or modify agent behavior
+through strongly-typed event callbacks.
+
+Example Usage:
+    ```python
+    from strands.hooks import HookProvider, HookRegistry
+    from strands.hooks.events import StartRequestEvent, EndRequestEvent
+
+    class LoggingHooks(HookProvider):
+        def register_hooks(self, registry: HookRegistry) -> None:
+            registry.add_callback(StartRequestEvent, self.log_start)
+            registry.add_callback(EndRequestEvent, self.log_end)
+
+        def log_start(self, event: StartRequestEvent) -> None:
+            print(f"Request started for {event.agent.name}")
+
+        def log_end(self, event: EndRequestEvent) -> None:
+            print(f"Request completed for {event.agent.name}")
+
+    # Use with agent
+    agent = Agent(hooks=[LoggingHooks()])
+    ```
+
+This replaces the older callback_handler approach with a more composable,
+type-safe system that supports multiple subscribers per event type.
+"""
+
+from .events import (
+    AfterInvocationEvent,
+    AgentInitializedEvent,
+    BeforeInvocationEvent,
+    MessageAddedEvent,
+)
+from .registry import HookCallback, HookEvent, HookProvider, HookRegistry
+
+__all__ = [
+    "AgentInitializedEvent",
+    "BeforeInvocationEvent",
+    "AfterInvocationEvent",
+    "MessageAddedEvent",
+    "HookEvent",
+    "HookProvider",
+    "HookCallback",
+    "HookRegistry",
+]