diff --git a/effectful/handlers/llm/completions.py b/effectful/handlers/llm/completions.py
index fc6ca47a..fd8e9eeb 100644
--- a/effectful/handlers/llm/completions.py
+++ b/effectful/handlers/llm/completions.py
@@ -160,8 +160,15 @@ def to_feedback_message(self, include_traceback: bool) -> Message:
 type MessageResult[T] = tuple[Message, typing.Sequence[DecodedToolCall], T | None]
 
 
+# prevent :func:`functools.wraps` from copying over `litellm.completion`'s type annotations,
+# which contains unresolvable forward references without import aiohttp
+_assn_without_type = [
+    attr for attr in functools.WRAPPER_ASSIGNMENTS if attr != "__annotations__"
+]
+
+
 @Operation.define
-@functools.wraps(litellm.completion)
+@functools.wraps(litellm.completion, assigned=_assn_without_type)
 def completion(*args, **kwargs) -> typing.Any:
     """Low-level LLM request. Handlers may log/modify requests and delegate via fwd().
 
@@ -172,6 +179,9 @@ def completion(*args, **kwargs) -> typing.Any:
     return litellm.completion(*args, **kwargs)
 
 
+del _assn_without_type
+
+
 @Operation.define
 def call_assistant[T, U](
     tools: collections.abc.Mapping[str, Tool],
@@ -490,3 +500,167 @@ def _call[**P, T](
             history.clear()
             history.update(history_copy)
         return typing.cast(T, result)
+
+
+class LoggingListener(typing.Protocol):
+    """Interface for observing :class:`Tool`, :class:`Template`, and
+    completion call events.
+
+    All methods are no-ops by default, allowing subclasses to
+    subscribe to only the events they care about.
+    """
+
+    def enter_tool_call[**P, Q](self, tool: Tool[P, Q]) -> None:
+        # can't just `pass` because that would mark the method as abstract
+        return None
+
+    def exit_tool_call[**P, Q](self, tool: Tool[P, Q], result: Q | None) -> None:
+        return None
+
+    def enter_template_call[**P, Q](self, template: Template[P, Q]) -> None:
+        return None
+
+    def exit_template_call[**P, Q](
+        self, template: Template[P, Q], result: Q | None
+    ) -> None:
+        return None
+
+    def enter_completion(self) -> None:
+        return None
+
+    def exit_completion(self, resp: typing.Any) -> None:
+        return None
+
+
+class LoggingHandler(ObjectInterpretation):
+    """Effect handler that wraps :class:`Tool`, :class:`Template`, and completion calls
+    and invokes callback functions registered in :attr:`listener`.
+
+    Compose with a provider via :func:`coproduct` or nested :func:`handler`
+    context managers to add logging without modifying the provider logic::
+
+        listener = ThinkingElapsedListener()
+        obs = LoggingHandler(listener)
+        with handler(provider), handler(obs):
+            result = my_template()
+    """
+
+    def __init__(self, listener: LoggingListener):
+        self.listener = listener
+
+    @implements(completion)
+    def _completion(self, *args, **kwargs) -> typing.Any:
+        self.listener.enter_completion()
+        response: typing.Any = None
+        try:
+            response = fwd(*args, **kwargs)
+            return response
+        finally:
+            self.listener.exit_completion(response)
+
+    @implements(Tool.__apply__)
+    def _call_tool[**P, T](
+        self, tool: Tool[P, T], *args: P.args, **kwargs: P.kwargs
+    ) -> T:
+        result_opt: T | None = None
+        try:
+            self.listener.enter_tool_call(tool)
+            result = typing.cast(T, fwd(tool, *args, **kwargs))
+            result_opt = result
+            return result
+        finally:
+            self.listener.exit_tool_call(tool, result_opt)
+
+    @implements(Template.__apply__)
+    def _call_template[**P, T](
+        self, template: Template[P, T], *args: P.args, **kwargs: P.kwargs
+    ) -> T:
+        result_opt: T | None = None
+        try:
+            self.listener.enter_template_call(template)
+            result = typing.cast(T, fwd(template, *args, **kwargs))
+            result_opt = result
+            return result
+        finally:
+            self.listener.exit_template_call(template, result_opt)
+
+
+class EmptyCallStackException(Exception):
+    """Raised when accessing the call stack is empty."""
+
+    pass
+
+
+class NoTemplateException(Exception):
+    """Raised when accessing the call stack does not have a :class:`Template`."""
+
+    pass
+
+
+@dataclasses.dataclass(frozen=True)
+class CallInfo[F: Tool[..., typing.Any]]:
+    func: F
+    info: dict[typing.Any, typing.Any]
+
+
+class CallStackListener(LoggingListener):
+    """Listener that maintains a call stack of active Tool and Template calls.
+
+    The call stack can be accessed directly through :attr:`callstack`.
+    The methods :meth:`current_function` and :meth:`current_template`
+    are provided for convenience to access the function (including
+    both templates and tools) or template that is currently executing
+    (i.e. on top of the call stack).
+    """
+
+    def __init__(self) -> None:
+        self.callstack: list[CallInfo[Tool[..., typing.Any]]] = []
+
+    @typing.override
+    def enter_tool_call[**P, Q](self, tool: Tool[P, Q]) -> None:
+        super().enter_tool_call(tool)
+        self.callstack.append(CallInfo(tool, {}))
+
+    @typing.override
+    def exit_tool_call[**P, Q](self, tool: Tool[P, Q], result: Q | None) -> None:
+        assert len(self.callstack) > 0 and tool is self.callstack[-1].func
+        self.callstack.pop()
+        super().exit_tool_call(tool, result)
+
+    @typing.override
+    def enter_template_call[**P, Q](self, template: Template[P, Q]) -> None:
+        super().enter_template_call(template)
+        self.callstack.append(CallInfo(template, {}))
+
+    @typing.override
+    def exit_template_call[**P, Q](
+        self, template: Template[P, Q], result: Q | None
+    ) -> None:
+        assert len(self.callstack) > 0 and template is self.callstack[-1].func
+        self.callstack.pop()
+        super().exit_template_call(template, result)
+
+    def current_func_info(self) -> CallInfo[Tool[..., typing.Any]]:
+        """Return the innermost active :class:`Tool` or :class:`Template`.
+
+        :raises EmptyCallStackException: if the call stack is empty.
+        """
+        try:
+            return self.callstack[-1]
+        except IndexError:
+            raise EmptyCallStackException()
+
+    def current_template_info(self) -> CallInfo[Template[..., typing.Any]]:
+        """Return the innermost active :class:`Template`, skipping any nested :class:`Tool`s.
+
+        :raises NoTemplateException: if no :class:`Template` is on the stack.
+        """
+        try:
+            # need to repack CallInfo to make the typechecker happy
+            return next(
+                CallInfo(ci.func, ci.info)
+                for ci in reversed(self.callstack)
+                if isinstance(ci.func, Template)
+            )
+        except StopIteration:
+            raise NoTemplateException()
diff --git a/obs-examples/thinking_elapsed.py b/obs-examples/thinking_elapsed.py
new file mode 100644
index 00000000..73c2cd9d
--- /dev/null
+++ b/obs-examples/thinking_elapsed.py
@@ -0,0 +1,125 @@
+import dataclasses
+
+from collections import defaultdict
+from functools import reduce
+from collections.abc import Callable
+from typing import Any, Hashable, override
+
+from effectful.handlers.llm import Tool, Template
+from effectful.ops.types import NotHandled
+from effectful.handlers.llm.completions import (
+    LiteLLMProvider, LoggingHandler, LoggingListener,
+    CallStackListener, CallInfo,
+)
+from effectful.ops.semantics import coproduct, handler
+from time import time
+
+
+@dataclasses.dataclass
+class ThinkingRecord:
+    """A single thinking/reasoning extraction paired with its source template."""
+    template: Template[..., Any]
+    reasoning_content: str | None
+    thinking_blocks: list[Any] | None
+
+
+class ThinkingListener(LoggingListener):
+    """Extracts thinking and reasoning content from litellm completion responses."""
+
+    def __init__(
+        self,
+        get_template_info: Callable[[], CallInfo[Template[..., Any]]],
+    ) -> None:
+        self.thinking_records: list[ThinkingRecord] = []
+        self._get_template_info = get_template_info
+
+    @override
+    def exit_completion(self, resp: Any) -> None:
+        if resp is not None:
+            message = resp.choices[0].message
+            reasoning_content = message.get("reasoning_content")
+            thinking_blocks = message.get("thinking_blocks")
+            if reasoning_content or thinking_blocks:
+                self.thinking_records.append(
+                    ThinkingRecord(
+                        template=self._get_template_info().func,
+                        reasoning_content=reasoning_content,
+                        thinking_blocks=thinking_blocks,
+                    )
+                )
+
+
+class ElapsedListener(LoggingListener):
+    """Tracks the elapsed time of each :class:`Template` call."""
+
+    def __init__(
+        self,
+        get_func_info: Callable[[], CallInfo[Tool[..., Any]]],
+    ) -> None:
+        self.elapsed: defaultdict[Hashable, float] = defaultdict(float)
+        self._get_func_info = get_func_info
+
+    @override
+    def enter_completion(self) -> None:
+        self._get_func_info().info['time'] = time()
+
+    @override
+    def exit_completion(self, resp: Any) -> None:
+        func_info = self._get_func_info()
+        time_elapsed = time() - func_info.info['time']
+        self.elapsed[func_info.func] += time_elapsed
+
+
+@Template.define
+def find_treasure() -> str:
+    """Ask Bob to find where the treasure is."""
+    raise NotHandled
+
+@Template.define
+def bob() -> str:
+    """Ask Alice to find where the treasure is."""
+    raise NotHandled
+
+@Tool.define
+def alice() -> str:
+    """Returns where the treasure is."""
+    return "school"
+
+@Template.define
+def pick_fruit() -> str:
+    """Return the name of a fruit."""
+    raise NotHandled
+
+
+def test_handler():
+    provider = LiteLLMProvider(
+        model='anthropic/claude-sonnet-4-20250514',
+        thinking={"type": "enabled", "budget_tokens": 1024}
+    )
+
+    callstack = CallStackListener()
+    thinking = ThinkingListener(callstack.current_template_info)
+    elapsed = ElapsedListener(callstack.current_func_info)
+
+    combined = reduce(coproduct, [
+        provider,
+        LoggingHandler(thinking),
+        LoggingHandler(elapsed),
+        LoggingHandler(callstack),
+    ])
+
+    with handler(combined):
+        print(pick_fruit())
+        print(find_treasure())
+
+        print('----------------------------------------')
+        for record in thinking.thinking_records:
+            print(record)
+
+        print('----------------------------------------')
+        for func, elapsed_time in elapsed.elapsed.items():
+            print(f"{func}:{elapsed_time:.2f}s")
+
+
+if __name__ == '__main__':
+    test_handler()
diff --git a/obs-examples/thinking_elapsed_multi.py b/obs-examples/thinking_elapsed_multi.py
new file mode 100644
index 00000000..2c249867
--- /dev/null
+++ b/obs-examples/thinking_elapsed_multi.py
@@ -0,0 +1,115 @@
+import dataclasses
+
+from collections import defaultdict
+from typing import Any, Hashable, override
+
+from effectful.handlers.llm import Tool, Template
+from effectful.ops.types import NotHandled
+from effectful.handlers.llm.completions import completion
+from effectful.ops.semantics import fwd, coproduct, handler
+from effectful.handlers.llm.completions import (
+    LiteLLMProvider, LoggingHandler, CallStackListener
+)
+from time import time
+
+
+@dataclasses.dataclass
+class ThinkingRecord:
+    """A single thinking/reasoning extraction paired with its source template."""
+    template: Template[...,Any]
+    reasoning_content: str | None
+    thinking_blocks: list[Any] | None
+
+
+class ThinkingListener(CallStackListener):
+    """Extracts thinking and reasoning content from litellm completion responses."""
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.thinking_records: list[ThinkingRecord] = []
+
+    @override
+    def exit_completion(self, resp: Any) -> None:
+        if resp is not None:
+            message = resp.choices[0].message
+            reasoning_content = message.get("reasoning_content")
+            thinking_blocks = message.get("thinking_blocks")
+            if reasoning_content or thinking_blocks:
+                self.thinking_records.append(
+                    ThinkingRecord(
+                        template=self.current_template_info().func,
+                        reasoning_content=reasoning_content,
+                        thinking_blocks=thinking_blocks,
+                    )
+                )
+        super().exit_completion(resp)
+
+class ElapsedListener(CallStackListener):
+    """Tracks the elapsed time of each :class:`Tool` or :class:`Template` call."""
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.elapsed:defaultdict[Hashable,float] = defaultdict(float)
+
+    @override
+    def enter_completion(self):
+        super().enter_completion()
+        self.current_func_info().info['time'] = time()
+
+    @override
+    def exit_completion(self, resp: Any) -> None:
+        time_elapsed = time() - self.current_func_info().info['time']
+        self.elapsed[self.current_func_info().func] += time_elapsed
+        super().exit_completion(resp)
+
+
+class ThinkingElapsedListener(ThinkingListener, ElapsedListener):
+    """Combines thinking extraction and elapsed time tracking."""
+    def __init__(self):
+        super().__init__()
+
+
+@Template.define
+def find_treasure() -> str:
+    """Ask Bob to find where the treasure is."""
+    raise NotHandled
+
+@Template.define
+def bob() -> str:
+    """Ask Alice to find where the treasure is."""
+    raise NotHandled
+
+@Tool.define
+def alice() -> str:
+    """Returns where the treasure is."""
+    return "school"
+
+@Template.define
+def pick_fruit() -> str:
+    """Return the name of a fruit."""
+    raise NotHandled
+
+def test_handler():
+    provider = LiteLLMProvider(
+        model='anthropic/claude-sonnet-4-20250514',
+        thinking={"type": "enabled", "budget_tokens": 1024}
+    )
+
+    listener = ThinkingElapsedListener()
+    obsprovider = LoggingHandler(listener)
+
+
+    with handler(provider), handler(obsprovider):
+        print(pick_fruit())
+        print(find_treasure())
+
+        print('----------------------------------------')
+        for thinking in listener.thinking_records:
+            print(thinking)
+
+        print('----------------------------------------')
+        for func, time in listener.elapsed.items():
+            print(f"{func}:{time:.2f}s")
+
+if __name__ == '__main__':
+    test_handler()