diff --git a/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.ml b/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.ml
index ae759cb8..ec73e9be 100644
--- a/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.ml
+++ b/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.ml
@@ -10,18 +10,31 @@ module Config = Config
 open Opentelemetry
 include Common_
 
-external reraise : exn -> 'a = "%reraise"
-(** This is equivalent to [Lwt.reraise]. We inline it here so we don't force to
-    use Lwt's latest version *)
-
 let needs_gc_metrics = Atomic.make false
 
 let last_gc_metrics = Atomic.make (Mtime_clock.now ())
 
 let timeout_gc_metrics = Mtime.Span.(20 * s)
 
-let gc_metrics = ref []
-(* side channel for GC, appended to {!E_metrics}'s data *)
+(* Cross domain thread-safe storage for GC metrics gathered from different fibres.
+   Ultimately appended to {!E_metrics}'s data on ticks. *)
+module GC_metrics : sig
+  val add : Proto.Metrics.resource_metrics -> unit
+  val drain : unit -> Proto.Metrics.resource_metrics list
+end
+= struct
+  (* Used to prevent data races across domains *)
+  let mutex = Eio.Mutex.create ()
+  let gc_metrics = ref []
+
+  let add m = Eio.Mutex.use_rw ~protect:true mutex (fun () ->
+      gc_metrics := m :: !gc_metrics)
+
+  let drain () = Eio.Mutex.use_rw ~protect:true mutex (fun () ->
+      let metrics = !gc_metrics in
+      gc_metrics := [];
+      metrics)
+end
 
 (* capture current GC metrics if {!needs_gc_metrics} is true,
    or it has been a long time since the last GC metrics collection,
@@ -40,7 +53,7 @@ let sample_gc_metrics_if_needed () =
         ~attrs:(Opentelemetry.GC_metrics.get_runtime_attributes ())
       @@ Opentelemetry.GC_metrics.get_metrics ()
     in
-    gc_metrics := l :: !gc_metrics
+    GC_metrics.add l
   )
 
 type error =
@@ -74,7 +87,10 @@ let report_err_ = function
 module Httpc : sig
   type t
 
-  val create : unit -> t
+  val create :
+    https:(Uri.t -> [ `Generic ] Eio.Net.stream_socket_ty r -> [> Eio.Flow.two_way_ty ] r) option ->
+    [> [> `Generic ] Eio.Net.ty ] r ->
+    t
 
   val send :
     t ->
@@ -88,15 +104,16 @@ end = struct
   open Opentelemetry.Proto
   module Httpc = Cohttp_eio.Client
 
-  type t = unit
+  type t = Httpc.t
 
-  let create () : t = ()
+  let create = Httpc.make
 
   let cleanup _self = ()
 
   (* send the content to the remote endpoint/path *)
-  let send (_self : t) ~url ~decode (bod : string) :
-      ('a, error) result Promise.t =
+  let send (client : t) ~url ~decode (bod : string) :
+      ('a, error) result (* TODO: Does this need to return a promise? *)=
+    Switch.run @@ fun sw ->
     let uri = Uri.of_string url in
 
     let open Cohttp in
@@ -108,7 +125,7 @@ end = struct
     let body = Cohttp_eio.Body.of_string bod in
     let r =
       try
-        let r = Httpc.post ~headers ~body uri in
+        let r = Httpc.post client ~sw  ~headers ~body uri in
         Ok r
       with e -> Error e
     in
@@ -121,7 +138,7 @@ end = struct
       in
       Error err
     | Ok (resp, body) ->
-      let body = Cohttp_lwt.Body.to_string body in
+      let body = Eio.Buf_read.(parse_exn take_all) body ~max_size:max_int in
       let code = Response.status resp |> Code.code_of_status in
       if not (Code.is_error code) then (
         match decode with
@@ -260,13 +277,15 @@ module type EMITTER = sig
   val cleanup : on_done:(unit -> unit) -> unit -> unit
 end
 
+(* Used by Switch.fail to signal when the collector is stopped. *)
+exception Collector_stopped
+
 (* make an emitter.
 
    exceptions inside should be caught, see
    https://opentelemetry.io/docs/reference/specification/error-handling/ *)
-let mk_emitter ~stop ~(config : Config.t) () : (module EMITTER) =
+let mk_emitter ~stop ~(config : Config.t) ~(net:_ Eio.Net.t) () : (module EMITTER) =
   let open Proto in
-  let open Lwt.Syntax in
   (* local helpers *)
   let open struct
     let timeout =
@@ -288,7 +307,7 @@ let mk_emitter ~stop ~(config : Config.t) () : (module EMITTER) =
 
     let set_on_tick_callbacks = Atomic.set on_tick_cbs_
 
-    let send_http_ (httpc : Httpc.t) encoder ~url ~encode x : unit Promise.t =
+    let send_http_ (httpc : Httpc.t) encoder ~url ~encode x : unit =
       Pbrt.Encoder.reset encoder;
       encode x encoder;
       let data = Pbrt.Encoder.to_string encoder in
@@ -336,23 +355,25 @@ let mk_emitter ~stop ~(config : Config.t) () : (module EMITTER) =
         ~encode:Logs_service.encode_pb_export_logs_service_request x
 
     (* emit metrics, if the batch is full or timeout lapsed *)
-    let emit_metrics_maybe ~now ?force httpc encoder : bool Promise.t =
+    let emit_metrics_maybe ~now ?force httpc encoder : bool =
       match Batch.pop_if_ready ?force ~now batch_metrics with
       | None -> false
-      | Some l ->
-        let batch = !gc_metrics :: l in
-        gc_metrics := [];
+      | Some collected_metrics ->
+        (* We take a large but fixed number of gc_metrics so that can't be trapped
+           forever waiting to exhaust a stream that is constantly being updated. *)
+        let gc_metrics = GC_metrics.drain () in
+        let batch = gc_metrics :: collected_metrics in
         let () = send_metrics_http httpc encoder batch in
         true
 
-    let emit_traces_maybe ~now ?force httpc encoder : bool Promise.t =
+    let emit_traces_maybe ~now ?force httpc encoder : bool =
       match Batch.pop_if_ready ?force ~now batch_traces with
       | None -> false
       | Some l ->
         let () = send_traces_http httpc encoder l in
         true
 
-    let emit_logs_maybe ~now ?force httpc encoder : bool Promise.t =
+    let emit_logs_maybe ~now ?force httpc encoder : bool  =
       match Batch.pop_if_ready ?force ~now batch_logs with
       | None -> false
       | Some l ->
@@ -367,16 +388,13 @@ let mk_emitter ~stop ~(config : Config.t) () : (module EMITTER) =
           "opentelemetry-curl: uncaught exception in %s: %s\n%s\n%!" where
           (Printexc.to_string e) bt
 
-    let emit_all_force (httpc : Httpc.t) encoder : unit Promise.t =
+    let emit_all_force (httpc : Httpc.t) encoder : unit =
       let now = Mtime_clock.now () in
-      let (_ : bool), ((_ : bool), (_ : bool)) =
-        Fiber.pair
-          (emit_logs_maybe ~now ~force:true httpc encoder)
-          (Fiber.pair
-             (emit_metrics_maybe ~now ~force:true httpc encoder)
-             (emit_traces_maybe ~now ~force:true httpc encoder))
-      in
-      ()
+      Fiber.all [
+        (fun () -> ignore @@ emit_logs_maybe ~now ~force:true httpc encoder);
+        (fun () -> ignore @@ emit_metrics_maybe ~now ~force:true httpc encoder);
+        (fun () -> ignore @@ emit_traces_maybe ~now ~force:true httpc encoder)
+      ]
 
     let tick_common_ () =
       if !debug_ then Printf.eprintf "tick (from %d)\n%!" (tid ());
@@ -391,23 +409,26 @@ let mk_emitter ~stop ~(config : Config.t) () : (module EMITTER) =
       ()
 
     (* thread that calls [tick()] regularly, to help enforce timeouts *)
-    let setup_ticker_thread ~tick ~finally () =
+    let setup_ticker_thread ~tick ~sw () : unit =
       let rec tick_thread () =
         if Atomic.get stop then
-          finally ()
+          Switch.fail sw Collector_stopped
         else (
           let () = Eio_unix.sleep 0.5 in
           let () = tick () in
           tick_thread ()
         )
       in
-      Fiber.fork ~sw
-        (* TODO: lwt-to-direct-style: [sw] must be propagated here. *)
-        tick_thread
+      Fiber.fork ~sw tick_thread
   end in
-  let httpc = Httpc.create () in
+  (* TODO: need https? *)
+  let httpc = Httpc.create ~https:None net in
   let encoder = Pbrt.Encoder.create () in
 
+  (* The entire module [M] shares the switch [sw]. This means that when the the
+     switch is cancelled, every thread started within the module will be cancelled
+     and have its resources disposed of. *)
+  Switch.run @@ fun sw ->
   let module M = struct
     (* we make sure that this is thread-safe, even though we don't have a
        background thread. There can still be a ticker thread, and there
@@ -419,7 +440,6 @@ let mk_emitter ~stop ~(config : Config.t) () : (module EMITTER) =
       Batch.push' batch_traces e;
       let now = Mtime_clock.now () in
       Fiber.fork ~sw
-        (* TODO: lwt-to-direct-style: [sw] must be propagated here. *)
         (fun () ->
           let (_ : bool) = emit_traces_maybe ~now httpc encoder in
           ())
@@ -430,7 +450,6 @@ let mk_emitter ~stop ~(config : Config.t) () : (module EMITTER) =
       Batch.push' batch_metrics e;
       let now = Mtime_clock.now () in
       Fiber.fork ~sw
-        (* TODO: lwt-to-direct-style: [sw] must be propagated here. *)
         (fun () ->
           let (_ : bool) = emit_metrics_maybe ~now httpc encoder in
           ())
@@ -440,7 +459,6 @@ let mk_emitter ~stop ~(config : Config.t) () : (module EMITTER) =
       Batch.push' batch_logs e;
       let now = Mtime_clock.now () in
       Fiber.fork ~sw
-        (* TODO: lwt-to-direct-style: [sw] must be propagated here. *)
         (fun () ->
           let (_ : bool) = emit_logs_maybe ~now httpc encoder in
           ())
@@ -451,42 +469,45 @@ let mk_emitter ~stop ~(config : Config.t) () : (module EMITTER) =
       tick_common_ ();
       sample_gc_metrics_if_needed ();
       let now = Mtime_clock.now () in
-      let (_ : bool), ((_ : bool), (_ : bool)) =
-        Fiber.pair
-          (emit_logs_maybe ~now httpc encoder)
-          (Fiber.pair
-             (emit_metrics_maybe ~now httpc encoder)
-             (emit_traces_maybe ~now httpc encoder))
-      in
-      ()
+      Fiber.all [
+        (fun () -> ignore @@ emit_logs_maybe ~now httpc encoder);
+        (fun () -> ignore @@ emit_metrics_maybe ~now httpc encoder);
+        (fun () -> ignore @@ emit_traces_maybe ~now httpc encoder)
+      ]
 
-    let () = setup_ticker_thread ~tick:tick_ ~finally:ignore ()
+    let () = setup_ticker_thread ~sw ~tick:tick_ ()
 
     (* if called in a blocking context: work in the background *)
     let tick () =
-      Fiber.fork ~sw
-        (* TODO: lwt-to-direct-style: [sw] must be propagated here. *)
-        tick_
+      Fiber.fork ~sw tick_
 
     let cleanup ~on_done () =
       if !debug_ then Printf.eprintf "opentelemetry: exiting…\n%!";
       Fiber.fork ~sw
-        (* TODO: lwt-to-direct-style: [sw] must be propagated here. *)
         (fun () ->
           let () = emit_all_force httpc encoder in
           Httpc.cleanup httpc;
           on_done ())
   end in
-  (module M)
+  (module M : EMITTER)
+
+(* Eio environment capabilities needed *)
+(* TODO: not able to supply just this type for env due to weak :( *)
+type 'a _env = 'a constraint 'a = <
+    net : _ Eio.Net.t; (** Network access *)
+  > as 'a
 
 module Backend
     (Arg : sig
       val stop : bool Atomic.t
 
+      (* Networking capability *)
+      val env : Eio_unix.Stdenv.base
+
       val config : Config.t
     end)
     () : Opentelemetry.Collector.BACKEND = struct
-  include (val mk_emitter ~stop:Arg.stop ~config:Arg.config ())
+  include (val mk_emitter ~stop:Arg.stop ~config:Arg.config ~net:Arg.env#net ())
 
   open Opentelemetry.Proto
   open Opentelemetry.Collector
@@ -578,48 +599,37 @@ module Backend
     }
 end
 
-let create_backend ?(stop = Atomic.make false) ?(config = Config.make ()) () =
+let create_backend ?(stop = Atomic.make false) ?(config = Config.make ()) (env : Eio_unix.Stdenv.base) =
   debug_ := config.debug;
 
   let module B =
     Backend
       (struct
+        let env = env
         let stop = stop
-
         let config = config
       end)
       ()
   in
   (module B : OT.Collector.BACKEND)
 
-let setup_ ?stop ?config () : unit =
-  let backend = create_backend ?stop ?config () in
+let setup_ ?stop ?config env : unit =
+  let backend = create_backend ?stop ?config env in
   OT.Collector.set_backend backend;
   ()
 
-let setup ?stop ?config ?(enable = true) () =
-  if enable then setup_ ?stop ?config ()
+let setup ?stop ?config ?(enable = true) env =
+  if enable then setup_ ?stop ?config env
 
-let remove_backend () : unit Promise.t =
-  let done_fut, done_u
-      (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
-      =
-    Promise.create ()
-  in
-  OT.Collector.remove_backend ~on_done:(fun () -> Promise.resolve done_u ()) ();
-  done_fut
+let remove_backend () =
+  OT.Collector.remove_backend ~on_done:ignore ()
 
-let with_setup ?stop ?(config = Config.make ()) ?(enable = true) () f :
-    _ Promise.t =
-  if enable then (
-    let open Lwt.Syntax in
-    setup_ ?stop ~config ();
-    try
-      let res = f () in
-      let () = remove_backend () in
-      res
-    with exn ->
-      let () = remove_backend () in
-      reraise exn
-  ) else
+(* TODO: Work thru stop logic to make sure it is sensible *)
+let with_setup ?stop ?(config = Config.make ()) ?(enable = true) env f =
+  Switch.run begin fun sw ->
+    if enable then (
+      setup_ ?stop ~config env;
+      Switch.on_release sw remove_backend
+    );
     f ()
+  end
diff --git a/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.mli b/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.mli
index c1dd53ad..86710fbd 100644
--- a/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.mli
+++ b/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.mli
@@ -15,14 +15,14 @@ module Config = Config
 val create_backend :
   ?stop:bool Atomic.t ->
   ?config:Config.t ->
-  unit ->
+  Eio_unix.Stdenv.base ->
   (module Opentelemetry.Collector.BACKEND)
 (** Create a new backend using lwt and cohttp
 
     NOTE [after_cleanup] optional parameter removed since NEXT_RELEASE *)
 
 val setup :
-  ?stop:bool Atomic.t -> ?config:Config.t -> ?enable:bool -> unit -> unit
+  ?stop:bool Atomic.t -> ?config:Config.t -> ?enable:bool -> Eio_unix.Stdenv.base -> unit
 (** Setup endpoint. This modifies {!Opentelemetry.Collector.backend}.
     @param enable
       actually setup the backend (default true). This can be used to
@@ -40,7 +40,7 @@ val with_setup :
   ?stop:bool Atomic.t ->
   ?config:Config.t ->
   ?enable:bool ->
-  unit ->
+  Eio_unix.Stdenv.base ->
   (unit -> 'a) ->
   'a
 (** [with_setup () f] is like [setup(); f()] but takes care of cleaning up after