diff --git a/src/litserve/callbacks/base.py b/src/litserve/callbacks/base.py
index 7a1dc7d0..9144bb7e 100644
--- a/src/litserve/callbacks/base.py
+++ b/src/litserve/callbacks/base.py
@@ -1,13 +1,12 @@
-import dataclasses
 import logging
 from abc import ABC
+from enum import Enum
 from typing import List, Union
 
 logger = logging.getLogger(__name__)
 
 
-@dataclasses.dataclass
-class EventTypes:
+class EventTypes(Enum):
     BEFORE_SETUP = "on_before_setup"
     AFTER_SETUP = "on_after_setup"
     BEFORE_DECODE_REQUEST = "on_before_decode_request"
diff --git a/src/litserve/callbacks/defaults/metric_callback.py b/src/litserve/callbacks/defaults/metric_callback.py
index f0065849..8782b615 100644
--- a/src/litserve/callbacks/defaults/metric_callback.py
+++ b/src/litserve/callbacks/defaults/metric_callback.py
@@ -1,23 +1,18 @@
 import time
 import typing
-from logging import getLogger
 
 from litserve.callbacks.base import Callback
 
 if typing.TYPE_CHECKING:
     from litserve import LitAPI
 
-logger = getLogger(__name__)
-
 
 class PredictionTimeLogger(Callback):
     def on_before_predict(self, lit_api: "LitAPI"):
-        t0 = time.perf_counter()
-        self._start_time = t0
+        self._start_time = time.perf_counter()
 
     def on_after_predict(self, lit_api: "LitAPI"):
-        t1 = time.perf_counter()
-        elapsed = t1 - self._start_time
+        elapsed = time.perf_counter() - self._start_time
         print(f"Prediction took {elapsed:.2f} seconds", flush=True)
 
 
diff --git a/src/litserve/loops/loops.py b/src/litserve/loops/loops.py
index 3959c471..5fbd3978 100644
--- a/src/litserve/loops/loops.py
+++ b/src/litserve/loops/loops.py
@@ -71,7 +71,7 @@ def inference_worker(
     callback_runner: CallbackRunner,
     loop: Union[str, _BaseLoop],
 ):
-    callback_runner.trigger_event(EventTypes.BEFORE_SETUP, lit_api=lit_api)
+    callback_runner.trigger_event(EventTypes.BEFORE_SETUP.value, lit_api=lit_api)
     try:
         lit_api.setup(device)
     except Exception:
@@ -79,7 +79,7 @@ def inference_worker(
         workers_setup_status[worker_id] = WorkerSetupStatus.ERROR
         return
     lit_api.device = device
-    callback_runner.trigger_event(EventTypes.AFTER_SETUP, lit_api=lit_api)
+    callback_runner.trigger_event(EventTypes.AFTER_SETUP.value, lit_api=lit_api)
 
     print(f"Setup complete for worker {worker_id}.")
 
diff --git a/src/litserve/loops/simple_loops.py b/src/litserve/loops/simple_loops.py
index e254835e..06323a51 100644
--- a/src/litserve/loops/simple_loops.py
+++ b/src/litserve/loops/simple_loops.py
@@ -68,29 +68,29 @@ def run_single_loop(
                 if hasattr(lit_spec, "populate_context"):
                     lit_spec.populate_context(context, x_enc)
 
-                callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST.value, lit_api=lit_api)
                 x = _inject_context(
                     context,
                     lit_api.decode_request,
                     x_enc,
                 )
-                callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST.value, lit_api=lit_api)
 
-                callback_runner.trigger_event(EventTypes.BEFORE_PREDICT, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_PREDICT.value, lit_api=lit_api)
                 y = _inject_context(
                     context,
                     lit_api.predict,
                     x,
                 )
-                callback_runner.trigger_event(EventTypes.AFTER_PREDICT, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_PREDICT.value, lit_api=lit_api)
 
-                callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE.value, lit_api=lit_api)
                 y_enc = _inject_context(
                     context,
                     lit_api.encode_response,
                     y,
                 )
-                callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE.value, lit_api=lit_api)
                 self.put_response(
                     transport=transport,
                     response_queue_id=response_queue_id,
@@ -135,29 +135,29 @@ async def _process_single_request(
             if hasattr(lit_spec, "populate_context"):
                 lit_spec.populate_context(context, x_enc)
 
-            callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST.value, lit_api=lit_api)
             x = await _async_inject_context(
                 context,
                 lit_api.decode_request,
                 x_enc,
             )
-            callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST.value, lit_api=lit_api)
 
-            callback_runner.trigger_event(EventTypes.BEFORE_PREDICT, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.BEFORE_PREDICT.value, lit_api=lit_api)
             y = await _async_inject_context(
                 context,
                 lit_api.predict,
                 x,
             )
-            callback_runner.trigger_event(EventTypes.AFTER_PREDICT, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.AFTER_PREDICT.value, lit_api=lit_api)
 
-            callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE.value, lit_api=lit_api)
             y_enc = await _async_inject_context(
                 context,
                 lit_api.encode_response,
                 y,
             )
-            callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE.value, lit_api=lit_api)
             self.put_response(
                 transport=transport,
                 response_queue_id=response_queue_id,
@@ -306,7 +306,7 @@ def run_batched_loop(
                     for input, context in zip(inputs, contexts):
                         lit_spec.populate_context(context, input)
 
-                callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST.value, lit_api=lit_api)
                 x = [
                     _inject_context(
                         context,
@@ -315,13 +315,13 @@ def run_batched_loop(
                     )
                     for input, context in zip(inputs, contexts)
                 ]
-                callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST.value, lit_api=lit_api)
 
                 x = lit_api.batch(x)
 
-                callback_runner.trigger_event(EventTypes.BEFORE_PREDICT, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_PREDICT.value, lit_api=lit_api)
                 y = _inject_context(contexts, lit_api.predict, x)
-                callback_runner.trigger_event(EventTypes.AFTER_PREDICT, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_PREDICT.value, lit_api=lit_api)
 
                 outputs = lit_api.unbatch(y)
 
@@ -332,12 +332,12 @@ def run_batched_loop(
                     )
                     raise HTTPException(500, "Batch size mismatch")
 
-                callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE.value, lit_api=lit_api)
                 y_enc_list = []
                 for response_queue_id, y, uid, context in zip(response_queue_ids, outputs, uids, contexts):
                     y_enc = _inject_context(context, lit_api.encode_response, y)
                     y_enc_list.append((response_queue_id, uid, y_enc))
-                callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE.value, lit_api=lit_api)
 
                 for response_queue_id, uid, y_enc in y_enc_list:
                     self.put_response(transport, response_queue_id, uid, y_enc, LitAPIStatus.OK)
diff --git a/src/litserve/loops/streaming_loops.py b/src/litserve/loops/streaming_loops.py
index 64032571..de3e295d 100644
--- a/src/litserve/loops/streaming_loops.py
+++ b/src/litserve/loops/streaming_loops.py
@@ -68,15 +68,15 @@ def run_streaming_loop(
                     x_enc,
                 )
 
-                callback_runner.trigger_event(EventTypes.BEFORE_PREDICT, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_PREDICT.value, lit_api=lit_api)
                 y_gen = _inject_context(
                     context,
                     lit_api.predict,
                     x,
                 )
-                callback_runner.trigger_event(EventTypes.AFTER_PREDICT, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_PREDICT.value, lit_api=lit_api)
 
-                callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE.value, lit_api=lit_api)
                 y_enc_gen = _inject_context(
                     context,
                     lit_api.encode_response,
@@ -87,8 +87,8 @@ def run_streaming_loop(
                     self.put_response(transport, response_queue_id, uid, y_enc, LitAPIStatus.OK)
                 self.put_response(transport, response_queue_id, uid, "", LitAPIStatus.FINISH_STREAMING)
 
-                callback_runner.trigger_event(EventTypes.AFTER_PREDICT, lit_api=lit_api)
-                callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_PREDICT.value, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE.value, lit_api=lit_api)
 
             except HTTPException as e:
                 self.put_response(
@@ -123,23 +123,23 @@ async def _process_streaming_request(
             if hasattr(lit_spec, "populate_context"):
                 lit_spec.populate_context(context, x_enc)
 
-            callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST.value, lit_api=lit_api)
             x = await _async_inject_context(
                 context,
                 lit_api.decode_request,
                 x_enc,
             )
-            callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST.value, lit_api=lit_api)
 
-            callback_runner.trigger_event(EventTypes.BEFORE_PREDICT, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.BEFORE_PREDICT.value, lit_api=lit_api)
             y_gen = await _async_inject_context(
                 context,
                 lit_api.predict,
                 x,
             )
-            callback_runner.trigger_event(EventTypes.AFTER_PREDICT, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.AFTER_PREDICT.value, lit_api=lit_api)
 
-            callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE.value, lit_api=lit_api)
 
             # When using async, predict should return an async generator
             # and encode_response should handle async generators
@@ -158,7 +158,7 @@ async def _process_streaming_request(
                     self.put_response(transport, response_queue_id, uid, y_enc, LitAPIStatus.OK)
 
             self.put_response(transport, response_queue_id, uid, "", LitAPIStatus.FINISH_STREAMING)
-            callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE, lit_api=lit_api)
+            callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE.value, lit_api=lit_api)
 
         except HTTPException as e:
             self.put_response(
@@ -282,7 +282,7 @@ def run_batched_streaming_loop(
                     for input, context in zip(inputs, contexts):
                         lit_spec.populate_context(context, input)
 
-                callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_DECODE_REQUEST.value, lit_api=lit_api)
                 x = [
                     _inject_context(
                         context,
@@ -291,19 +291,19 @@ def run_batched_streaming_loop(
                     )
                     for input, context in zip(inputs, contexts)
                 ]
-                callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_DECODE_REQUEST.value, lit_api=lit_api)
 
                 x = lit_api.batch(x)
 
-                callback_runner.trigger_event(EventTypes.BEFORE_PREDICT, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_PREDICT.value, lit_api=lit_api)
                 y_iter = _inject_context(contexts, lit_api.predict, x)
-                callback_runner.trigger_event(EventTypes.AFTER_PREDICT, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_PREDICT.value, lit_api=lit_api)
 
                 unbatched_iter = lit_api.unbatch(y_iter)
 
-                callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.BEFORE_ENCODE_RESPONSE.value, lit_api=lit_api)
                 y_enc_iter = _inject_context(contexts, lit_api.encode_response, unbatched_iter)
-                callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE, lit_api=lit_api)
+                callback_runner.trigger_event(EventTypes.AFTER_ENCODE_RESPONSE.value, lit_api=lit_api)
 
                 # y_enc_iter -> [[response-1, response-2], [response-1, response-2]]
                 for y_batch in y_enc_iter:
diff --git a/src/litserve/server.py b/src/litserve/server.py
index 168268ae..29017687 100644
--- a/src/litserve/server.py
+++ b/src/litserve/server.py
@@ -369,7 +369,7 @@ async def lifespan(self, app: FastAPI):
         try:
             yield
         finally:
-            self._callback_runner.trigger_event(EventTypes.ON_SERVER_END, litserver=self)
+            self._callback_runner.trigger_event(EventTypes.ON_SERVER_END.value, litserver=self)
 
             # Cancel the task
             task.cancel()
@@ -412,7 +412,7 @@ def active_requests(self):
 
     def register_endpoints(self):
         """Register endpoint routes for the FastAPI app and setup middlewares."""
-        self._callback_runner.trigger_event(EventTypes.ON_SERVER_START, litserver=self)
+        self._callback_runner.trigger_event(EventTypes.ON_SERVER_START.value, litserver=self)
         workers_ready = False
 
         @self.app.get("/", dependencies=[Depends(self.setup_auth())])
@@ -449,7 +449,7 @@ async def info(request: Request) -> Response:
 
         async def predict(request: self.request_type) -> self.response_type:
             self._callback_runner.trigger_event(
-                EventTypes.ON_REQUEST,
+                EventTypes.ON_REQUEST.value,
                 active_requests=self.active_requests,
                 litserver=self,
             )
@@ -478,12 +478,12 @@ async def predict(request: self.request_type) -> self.response_type:
             if status == LitAPIStatus.ERROR:
                 logger.error("Error in request: %s", response)
                 raise HTTPException(status_code=500)
-            self._callback_runner.trigger_event(EventTypes.ON_RESPONSE, litserver=self)
+            self._callback_runner.trigger_event(EventTypes.ON_RESPONSE.value, litserver=self)
             return response
 
         async def stream_predict(request: self.request_type) -> self.response_type:
             self._callback_runner.trigger_event(
-                EventTypes.ON_REQUEST,
+                EventTypes.ON_REQUEST.value,
                 active_requests=self.active_requests,
                 litserver=self,
             )
@@ -502,7 +502,7 @@ async def stream_predict(request: self.request_type) -> self.response_type:
             response = call_after_stream(
                 self.data_streamer(q, data_available=event),
                 self._callback_runner.trigger_event,
-                EventTypes.ON_RESPONSE,
+                EventTypes.ON_RESPONSE.value,
                 litserver=self,
             )
             return StreamingResponse(response)
diff --git a/tests/test_callbacks.py b/tests/test_callbacks.py
index a374ef4c..27740c88 100644
--- a/tests/test_callbacks.py
+++ b/tests/test_callbacks.py
@@ -58,8 +58,8 @@ def test_metric_logger(capfd):
     cb_runner = CallbackRunner()
     cb_runner._add_callbacks(cb)
     assert cb_runner._callbacks == [cb], "Callback not added to runner"
-    cb_runner.trigger_event(EventTypes.BEFORE_PREDICT, lit_api=None)
-    cb_runner.trigger_event(EventTypes.AFTER_PREDICT, lit_api=None)
+    cb_runner.trigger_event(EventTypes.BEFORE_PREDICT.value, lit_api=None)
+    cb_runner.trigger_event(EventTypes.AFTER_PREDICT.value, lit_api=None)
 
     captured = capfd.readouterr()
     pattern = r"Prediction took \d+\.\d{2} seconds"