diff --git a/dune-project b/dune-project
index 44135a7..ca2dd7d 100644
--- a/dune-project
+++ b/dune-project
@@ -72,6 +72,7 @@
    (>= 2.0))
   base-unix
   dune)
+ (depopts lwt)
  (tags
   (trace tracing catapult TEF chrome-format chrome-trace json)))
 
diff --git a/src/tef/emit_tef.ml b/src/tef/emit_tef.ml
deleted file mode 100644
index e69de29..0000000
diff --git a/src/tef/lwt/common_.ml b/src/tef/lwt/common_.ml
new file mode 100644
index 0000000..a613fa1
--- /dev/null
+++ b/src/tef/lwt/common_.ml
@@ -0,0 +1,5 @@
+module Sub = Trace_subscriber
+module A = Trace_core.Internal_.Atomic_
+include Lwt.Syntax
+
+let ( let@ ) = ( @@ )
diff --git a/src/tef/lwt/dune b/src/tef/lwt/dune
new file mode 100644
index 0000000..37177ce
--- /dev/null
+++ b/src/tef/lwt/dune
@@ -0,0 +1,15 @@
+
+(library
+ (name trace_tef_lwt)
+ (public_name trace-tef.lwt)
+ (optional) ; lwt
+ (libraries
+  trace.core
+  trace.private.util
+  trace.subscriber
+  trace-tef
+  mtime
+  mtime.clock.os
+  unix
+  lwt
+  lwt.unix))
diff --git a/src/tef/lwt/exporter.ml b/src/tef/lwt/exporter.ml
new file mode 100644
index 0000000..a324f3c
--- /dev/null
+++ b/src/tef/lwt/exporter.ml
@@ -0,0 +1,88 @@
+(** An exporter, takes JSON objects and writes them somewhere *)
+
+open Common_
+
+type t = {
+  on_json: Buffer.t -> unit;
+      (** Takes a buffer and writes it somewhere. The buffer is only valid
+          during this call and must not be stored. *)
+  flush: unit -> unit;  (** Force write *)
+  close: unit -> unit;  (** Close underlying resources *)
+}
+(** An exporter, takes JSON objects and writes them somewhere.
+
+    This should be thread-safe if used in a threaded environment. *)
+
+open struct
+  let with_lock lock f =
+    Mutex.lock lock;
+    try
+      let res = f () in
+      Mutex.unlock lock;
+      res
+    with e ->
+      let bt = Printexc.get_raw_backtrace () in
+      Mutex.unlock lock;
+      Printexc.raise_with_backtrace e bt
+end
+
+(** Export to the lwt channel *)
+let of_lwt_output_channel ~close_channel ~jsonl (oc: Lwt_io.output_channel) : t 
+
+(** Export to the channel
+    @param jsonl
+      if true, export as a JSON object per line, otherwise export as a single
+      big JSON array.
+    @param close_channel if true, closing the exporter will close the channel *)
+let of_out_channel ~close_channel ~jsonl oc : t =
+  let lock = Mutex.create () in
+  let first = ref true in
+  let closed = ref false in
+  let flush () =
+    let@ () = with_lock lock in
+    flush oc
+  in
+  let close () =
+    let@ () = with_lock lock in
+    if not !closed then (
+      closed := true;
+      if not jsonl then output_char oc ']';
+      if close_channel then close_out_noerr oc
+    )
+  in
+  let on_json buf =
+    let@ () = with_lock lock in
+    if not jsonl then
+      if !first then (
+        if not jsonl then output_char oc '[';
+        first := false
+      ) else
+        output_string oc ",\n";
+    Buffer.output_buffer oc buf;
+    if jsonl then output_char oc '\n'
+  in
+  { flush; close; on_json }
+
+let of_buffer ~jsonl (buf : Buffer.t) : t =
+  let lock = Mutex.create () in
+  let first = ref true in
+  let closed = ref false in
+  let close () =
+    let@ () = with_lock lock in
+    if not !closed then (
+      closed := true;
+      if not jsonl then Buffer.add_char buf ']'
+    )
+  in
+  let on_json json =
+    let@ () = with_lock lock in
+    if not jsonl then
+      if !first then (
+        if not jsonl then Buffer.add_char buf '[';
+        first := false
+      ) else
+        Buffer.add_string buf ",\n";
+    Buffer.add_buffer buf json;
+    if jsonl then Buffer.add_char buf '\n'
+  in
+  { flush = ignore; close; on_json }
diff --git a/src/tef/lwt/suscriber.ml b/src/tef/lwt/suscriber.ml
new file mode 100644
index 0000000..df70340
--- /dev/null
+++ b/src/tef/lwt/suscriber.ml
@@ -0,0 +1 @@
+include Trace_tef.Subscriber
diff --git a/src/tef/lwt/trace_tef_lwt.ml b/src/tef/lwt/trace_tef_lwt.ml
new file mode 100644
index 0000000..39b9c06
--- /dev/null
+++ b/src/tef/lwt/trace_tef_lwt.ml
@@ -0,0 +1,142 @@
+open Trace_core
+module Subscriber = Subscriber
+module Exporter = Exporter
+module Writer = Writer
+
+let block_signals () =
+  try
+    ignore
+      (Unix.sigprocmask SIG_BLOCK
+         [
+           Sys.sigterm;
+           Sys.sigpipe;
+           Sys.sigint;
+           Sys.sigchld;
+           Sys.sigalrm;
+           Sys.sigusr1;
+           Sys.sigusr2;
+         ]
+        : _ list)
+  with _ -> ()
+
+(** Thread that simply regularly "ticks", sending events to the background
+    thread so it has a chance to write to the file *)
+let tick_thread (sub : Subscriber.t) : unit =
+  block_signals ();
+  while Subscriber.active sub do
+    Thread.delay 0.5;
+    Subscriber.flush sub
+  done
+
+type output =
+  [ `Stdout
+  | `Stderr
+  | `File of string
+  ]
+
+let subscriber_ ~finally ~out ~(mode : [ `Single | `Jsonl ]) () :
+    Trace_subscriber.t =
+  let jsonl = mode = `Jsonl in
+  let oc, must_close =
+    match out with
+    | `Stdout -> stdout, false
+    | `Stderr -> stderr, false
+    | `File path -> open_out path, true
+    | `File_append path ->
+      open_out_gen [ Open_creat; Open_wronly; Open_append ] 0o644 path, true
+    | `Output oc -> oc, false
+  in
+  let pid =
+    if !Trace_subscriber.Private_.mock then
+      2
+    else
+      Unix.getpid ()
+  in
+
+  let exporter = Exporter.of_out_channel oc ~jsonl ~close_channel:must_close in
+  let exporter =
+    {
+      exporter with
+      close =
+        (fun () ->
+          exporter.close ();
+          finally ());
+    }
+  in
+  let sub = Subscriber.create ~pid ~exporter () in
+  let _t_tick : Thread.t = Thread.create tick_thread sub in
+  Subscriber.subscriber sub
+
+let collector_ ~(finally : unit -> unit) ~(mode : [ `Single | `Jsonl ]) ~out ()
+    : collector =
+  let sub = subscriber_ ~finally ~mode ~out () in
+  Trace_subscriber.collector sub
+
+let[@inline] subscriber ~out () : Trace_subscriber.t =
+  subscriber_ ~finally:ignore ~mode:`Single ~out ()
+
+let[@inline] collector ~out () : collector =
+  collector_ ~finally:ignore ~mode:`Single ~out ()
+
+open struct
+  let register_atexit =
+    let has_registered = ref false in
+    fun () ->
+      if not !has_registered then (
+        has_registered := true;
+        at_exit Trace_core.shutdown
+      )
+end
+
+let setup ?(out = `Env) () =
+  register_atexit ();
+  match out with
+  | `Stderr -> Trace_core.setup_collector @@ collector ~out:`Stderr ()
+  | `Stdout -> Trace_core.setup_collector @@ collector ~out:`Stdout ()
+  | `File path -> Trace_core.setup_collector @@ collector ~out:(`File path) ()
+  | `Env ->
+    (match Sys.getenv_opt "TRACE" with
+    | Some ("1" | "true") ->
+      let path = "trace.json" in
+      let c = collector ~out:(`File path) () in
+      Trace_core.setup_collector c
+    | Some "stdout" -> Trace_core.setup_collector @@ collector ~out:`Stdout ()
+    | Some "stderr" -> Trace_core.setup_collector @@ collector ~out:`Stderr ()
+    | Some path ->
+      let c = collector ~out:(`File path) () in
+      Trace_core.setup_collector c
+    | None -> ())
+
+let with_setup ?out () f =
+  setup ?out ();
+  Fun.protect ~finally:Trace_core.shutdown f
+
+module Mock_ = struct
+  let now = ref 0
+
+  (* used to mock timing *)
+  let get_now_ns () : int64 =
+    let x = !now in
+    incr now;
+    Int64.(mul (of_int x) 1000L)
+
+  let get_tid_ () : int = 3
+end
+
+module Private_ = struct
+  let mock_all_ () =
+    Trace_subscriber.Private_.mock := true;
+    Trace_subscriber.Private_.get_now_ns_ := Mock_.get_now_ns;
+    Trace_subscriber.Private_.get_tid_ := Mock_.get_tid_;
+    ()
+
+  let on_tracing_error = Subscriber.on_tracing_error
+
+  let subscriber_jsonl ~finally ~out () =
+    subscriber_ ~finally ~mode:`Jsonl ~out ()
+
+  let collector_jsonl ~finally ~out () : collector =
+    collector_ ~finally ~mode:`Jsonl ~out ()
+
+  module Event = Event
+end
diff --git a/src/tef/lwt/trace_tef_lwt.mli b/src/tef/lwt/trace_tef_lwt.mli
new file mode 100644
index 0000000..9cf8dd1
--- /dev/null
+++ b/src/tef/lwt/trace_tef_lwt.mli
@@ -0,0 +1,66 @@
+module Subscriber = Subscriber
+module Exporter = Exporter
+module Writer = Writer
+
+type output =
+  [ `Stdout
+  | `Stderr
+  | `File of string
+  ]
+(** Output for tracing.
+
+    - [`Stdout] will enable tracing and print events on stdout
+    - [`Stderr] will enable tracing and print events on stderr
+    - [`File "foo"] will enable tracing and print events into file named "foo"
+*)
+
+val subscriber : out:[< output ] -> unit -> Trace_subscriber.t
+(** A subscriber emitting TEF traces into [out].
+    @since 0.8 *)
+
+val collector : out:[< output ] -> unit -> Trace_core.collector
+(** Make a collector that writes into the given output. See {!setup} for more
+    details. *)
+
+val setup : ?out:[ output | `Env ] -> unit -> unit
+(** [setup ()] installs the collector depending on [out].
+
+    @param out
+      can take different values:
+      - regular {!output} value to specify where events go
+      - [`Env] will enable tracing if the environment variable "TRACE" is set.
+
+    - If it's set to "1", then the file is "trace.json".
+    - If it's set to "stdout", then logging happens on stdout (since 0.2)
+    - If it's set to "stderr", then logging happens on stdout (since 0.2)
+    - Otherwise, if it's set to a non empty string, the value is taken to be the
+      file path into which to write. *)
+
+val with_setup : ?out:[ output | `Env ] -> unit -> (unit -> 'a) -> 'a
+(** [with_setup () f] (optionally) sets a collector up, calls [f()], and makes
+    sure to shutdown before exiting. since 0.2 a () argument was added. *)
+
+(**/**)
+
+module Private_ : sig
+  val mock_all_ : unit -> unit
+  (** use fake, deterministic timestamps, TID, PID *)
+
+  val on_tracing_error : (string -> unit) ref
+
+  val subscriber_jsonl :
+    finally:(unit -> unit) ->
+    out:[ `File_append of string | `Output of out_channel ] ->
+    unit ->
+    Trace_subscriber.t
+
+  val collector_jsonl :
+    finally:(unit -> unit) ->
+    out:[ `File_append of string | `Output of out_channel ] ->
+    unit ->
+    Trace_core.collector
+
+  module Event = Event
+end
+
+(**/**)
diff --git a/src/tef/lwt/writer.ml b/src/tef/lwt/writer.ml
new file mode 100644
index 0000000..747a6b6
--- /dev/null
+++ b/src/tef/lwt/writer.ml
@@ -0,0 +1 @@
+include Trace_tef.Writer