diff --git a/devkit.opam b/devkit.opam
index 25301de..3708d79 100644
--- a/devkit.opam
+++ b/devkit.opam
@@ -17,11 +17,12 @@ depends: [
   "ounit2"
   "camlzip"
   "libevent" {>= "0.8.0"}
-  "ocurl" {>= "0.7.2"}
+  "curl" {>= "0.10.0"}
+  "curl_lwt"
   "pcre2" {>= "8.0.3"}
-  "trace" {>= "0.4"}
+  "trace" {>= "0.12"}
   "extunix" {>= "0.1.4"}
-  "lwt" {>= "5.7.0"}
+  "lwt" {>= "6.0.0"}
   "lwt_ppx"
   "base-bytes"
   "base-unix"
diff --git a/lwt_engines.ml b/lwt_engines.ml
index 3802e29..9cf06c4 100644
--- a/lwt_engines.ml
+++ b/lwt_engines.ml
@@ -30,6 +30,8 @@ method poll fds timeout =
   l
 end
 
+type Lwt_engine.engine_id += Engine_id__Devkit_libevent
+
 (** libevent-based engine for lwt *)
 class libevent =
 let once_block = Ev.[ONCE] in
@@ -37,6 +39,8 @@ let once_nonblock = Ev.[ONCE;NONBLOCK] in
 object(self)
   inherit Lwt_engine.abstract
 
+  method id = Engine_id__Devkit_libevent
+
   val events_ = Ev.init ()
   val mutable pid = Unix.getpid ()
   method events =
diff --git a/possibly_otel.mli b/possibly_otel.mli
index d880365..5179fe9 100644
--- a/possibly_otel.mli
+++ b/possibly_otel.mli
@@ -2,7 +2,7 @@ module Otrace := Trace_core
 
 module Traceparent : sig
   val name : string
-  val get_ambient : ?explicit_span:Trace_core.explicit_span -> unit -> string option
+  val get_ambient : ?explicit_span:Trace_core.span -> unit -> string option
 end
 
 val enter_manual_span :
@@ -11,4 +11,4 @@ val enter_manual_span :
   __LINE__:int ->
   ?data:(unit -> (string * Otrace.user_data) list) ->
   string ->
-  Trace_core.explicit_span
+  Trace_core.span
diff --git a/possibly_otel.real.ml b/possibly_otel.real.ml
index f56d67c..50e6e7f 100644
--- a/possibly_otel.real.ml
+++ b/possibly_otel.real.ml
@@ -5,22 +5,10 @@ let (let*) o f = Option.map f o
 module Traceparent = struct
   let name = Trace_context.Traceparent.name
 
-  let get_ambient ?explicit_span () =
+  let get_ambient ?explicit_span:_ () =
     let* Scope.{ trace_id; span_id; _ } = Scope.get_ambient_scope () in
-    let span_id = match explicit_span with
-      | Some {Trace_core.span; _} -> Opentelemetry_trace.Internal.otel_of_otrace span
-      | None -> span_id 
-    in
     Trace_context.Traceparent.to_value ~trace_id ~parent_id:span_id ()
 end
 
 let enter_manual_span ~__FUNCTION__ ~__FILE__ ~__LINE__ ?data name =
-    match Scope.get_ambient_scope () with
-    | None ->
-      Trace_core.enter_manual_toplevel_span ~__FUNCTION__ ~__FILE__ ~__LINE__ ?data name
-    | Some Scope.{ span_id; _ } ->
-      let otrace_espan = Trace_core.{
-        span = Opentelemetry_trace.Internal.otrace_of_otel span_id;
-        meta = Trace_core.Meta_map.empty
-      } in
-      Trace_core.enter_manual_sub_span ~parent:otrace_espan ~__FUNCTION__ ~__FILE__ ~__LINE__ ?data name
+      Trace_core.enter_span ~parent:None ~__FUNCTION__ ~__FILE__ ~__LINE__ ?data name
diff --git a/possibly_otel.stub.ml b/possibly_otel.stub.ml
index 2afe916..18f8d15 100644
--- a/possibly_otel.stub.ml
+++ b/possibly_otel.stub.ml
@@ -6,4 +6,4 @@ end
 
 
 let enter_manual_span ~__FUNCTION__ ~__FILE__ ~__LINE__ ?data name =
-  Trace_core.enter_manual_toplevel_span ~__FUNCTION__ ~__FILE__ ~__LINE__ ?data name
+  Trace_core.enter_manual_span ~parent:None ~__FUNCTION__ ~__FILE__ ~__LINE__ ?data name
diff --git a/prelude.ml b/prelude.ml
index ec457e2..c13e44a 100644
--- a/prelude.ml
+++ b/prelude.ml
@@ -61,6 +61,13 @@ let call_me_maybe f x =
   and poll is guaranteed to be available without the fd limitation.
 *)
 let () =
-  if not (Lwt_config._HAVE_LIBEV && Lwt_config.libev_default) then begin
+  match Lwt_engine.id () with
+  | Lwt_engine.Engine_id__libev _ -> ()
+  | Lwt_engine.Engine_id__select ->
+    (* Otherwise, prefer poll over select, because select can only monitor fds up to 1024,
+       and poll is guaranteed to be available without the fd limitation. *)
     Lwt_engine.set @@ new Lwt_engines.poll
-  end
+  | Lwt_engine.Engine_id__poll -> ()
+  | lwteng ->
+      eprintfn "Unknown Lwt engine (%s) in use, leaving as is" Obj.Extension_constructor.(name (of_val lwteng));
+      ()
diff --git a/web.ml b/web.ml
index 9431236..da01ce0 100644
--- a/web.ml
+++ b/web.ml
@@ -321,8 +321,8 @@ module Http (IO : IO_TYPE) (Curl_IO : CURL with type 'a t = 'a IO.t) : HTTP with
     let t = new Action.timer in
     let result = Some (fun h code ->
       if verbose then verbose_curl_result nr_http action t h code;
-      Trace_core.add_data_to_manual_span explicit_span ["http.response.status_code", `Int (Curl.get_httpcode h)];
-      Trace_core.exit_manual_span explicit_span;
+      Trace_core.add_data_to_span explicit_span ["http.response.status_code", `Int (Curl.get_httpcode h)];
+      Trace_core.exit_span explicit_span;
       return ()
     ) in