diff --git a/langfuse/api/legacy/observations_v1/client.py b/langfuse/api/legacy/observations_v1/client.py
index 871191ee5..fc7f37b48 100644
--- a/langfuse/api/legacy/observations_v1/client.py
+++ b/langfuse/api/legacy/observations_v1/client.py
@@ -35,6 +35,7 @@ def get(
         self,
         observation_id: str,
         *,
+        start_time: typing.Optional[dt.datetime] = None,
         request_options: typing.Optional[RequestOptions] = None,
     ) -> ObservationsViewSingle:
         """
@@ -45,6 +46,9 @@ def get(
         observation_id : str
             The unique langfuse identifier of an observation, can be an event, span or generation
 
+        start_time : typing.Optional[dt.datetime]
+            The start time of the observation (ISO 8601 with offset, e.g. 2024-01-01T00:00:00Z). When provided, the lookup is restricted to the observation's start day, which makes the request substantially faster. Omit it to look up the observation without a time bound.
+
         request_options : typing.Optional[RequestOptions]
             Request-specific configuration.
 
@@ -69,7 +73,7 @@ def get(
         )
         """
         _response = self._raw_client.get(
-            observation_id, request_options=request_options
+            observation_id, start_time=start_time, request_options=request_options
         )
         return _response.data
 
@@ -291,6 +295,7 @@ async def get(
         self,
         observation_id: str,
         *,
+        start_time: typing.Optional[dt.datetime] = None,
         request_options: typing.Optional[RequestOptions] = None,
     ) -> ObservationsViewSingle:
         """
@@ -301,6 +306,9 @@ async def get(
         observation_id : str
             The unique langfuse identifier of an observation, can be an event, span or generation
 
+        start_time : typing.Optional[dt.datetime]
+            The start time of the observation (ISO 8601 with offset, e.g. 2024-01-01T00:00:00Z). When provided, the lookup is restricted to the observation's start day, which makes the request substantially faster. Omit it to look up the observation without a time bound.
+
         request_options : typing.Optional[RequestOptions]
             Request-specific configuration.
 
@@ -333,7 +341,7 @@ async def main() -> None:
         asyncio.run(main())
         """
         _response = await self._raw_client.get(
-            observation_id, request_options=request_options
+            observation_id, start_time=start_time, request_options=request_options
         )
         return _response.data
 
diff --git a/langfuse/api/legacy/observations_v1/raw_client.py b/langfuse/api/legacy/observations_v1/raw_client.py
index 73343c130..9023dce56 100644
--- a/langfuse/api/legacy/observations_v1/raw_client.py
+++ b/langfuse/api/legacy/observations_v1/raw_client.py
@@ -34,6 +34,7 @@ def get(
         self,
         observation_id: str,
         *,
+        start_time: typing.Optional[dt.datetime] = None,
         request_options: typing.Optional[RequestOptions] = None,
     ) -> HttpResponse[ObservationsViewSingle]:
         """
@@ -44,6 +45,9 @@ def get(
         observation_id : str
             The unique langfuse identifier of an observation, can be an event, span or generation
 
+        start_time : typing.Optional[dt.datetime]
+            The start time of the observation (ISO 8601 with offset, e.g. 2024-01-01T00:00:00Z). When provided, the lookup is restricted to the observation's start day, which makes the request substantially faster. Omit it to look up the observation without a time bound.
+
         request_options : typing.Optional[RequestOptions]
             Request-specific configuration.
 
@@ -54,6 +58,11 @@ def get(
         _response = self._client_wrapper.httpx_client.request(
             f"api/public/observations/{jsonable_encoder(observation_id)}",
             method="GET",
+            params={
+                "startTime": serialize_datetime(start_time)
+                if start_time is not None
+                else None,
+            },
             request_options=request_options,
         )
         try:
@@ -411,6 +420,7 @@ async def get(
         self,
         observation_id: str,
         *,
+        start_time: typing.Optional[dt.datetime] = None,
         request_options: typing.Optional[RequestOptions] = None,
     ) -> AsyncHttpResponse[ObservationsViewSingle]:
         """
@@ -421,6 +431,9 @@ async def get(
         observation_id : str
             The unique langfuse identifier of an observation, can be an event, span or generation
 
+        start_time : typing.Optional[dt.datetime]
+            The start time of the observation (ISO 8601 with offset, e.g. 2024-01-01T00:00:00Z). When provided, the lookup is restricted to the observation's start day, which makes the request substantially faster. Omit it to look up the observation without a time bound.
+
         request_options : typing.Optional[RequestOptions]
             Request-specific configuration.
 
@@ -431,6 +444,11 @@ async def get(
         _response = await self._client_wrapper.httpx_client.request(
             f"api/public/observations/{jsonable_encoder(observation_id)}",
             method="GET",
+            params={
+                "startTime": serialize_datetime(start_time)
+                if start_time is not None
+                else None,
+            },
             request_options=request_options,
         )
         try: