diff --git a/src/subscriber/callbacks.ml b/src/subscriber/callbacks.ml
deleted file mode 100644
index 6e80816..0000000
--- a/src/subscriber/callbacks.ml
+++ /dev/null
@@ -1,114 +0,0 @@
-(** Callbacks used for subscribers.
-
-    Each subscriber defines a set of callbacks, for each possible tracing event.
-    These callbacks take a custom state that is paired with the callbacks in
-    {!Subscriber.t}.
-
-    To use a default implementation for some callbacks, use:
-
-    {[
-      module My_callbacks = struct
-        type st = …
-
-        include Trace_subscriber.Callbacks.Dummy
-
-        let on_init (state:st) ~time_ns : unit = …
-
-        (* … other custom callbacks … *)
-      end
-    ]}
-
-    {b NOTE}: the [trace_id] passed alongside manual spans is guaranteed to be
-    at least 64 bits. *)
-
-open Trace_core
-
-type 'st t = {
-  on_init: 'st -> time_ns:int64 -> unit;
-      (** Called when the subscriber is initialized in a collector *)
-  new_span_id: 'st -> Span_sub.span_id;
-      (** How to generate a new span ID?
-          @since NEXT_RELEASE *)
-  new_trace_id: 'st -> Span_sub.trace_id;
-      (** How to generate a new trace ID?
-          @since NEXT_RELEASE *)
-  on_shutdown: 'st -> time_ns:int64 -> unit;
-      (** Called when the collector is shutdown *)
-  on_enter_span: 'st -> Span_sub.t -> unit;  (** Enter a span *)
-  on_exit_span: 'st -> time_ns:int64 -> tid:int -> Span_sub.t -> unit;
-      (** Exit a span. This and [on_enter_span] must follow strict stack
-          discipline.
-          @param tid the id of the thread on which the span was exited. *)
-  on_message:
-    'st ->
-    time_ns:int64 ->
-    tid:int ->
-    span:Span_sub.t option ->
-    params:extension_parameter list ->
-    data:(string * Trace_core.user_data) list ->
-    string ->
-    unit;
-      (** Emit a log message *)
-  on_counter:
-    'st ->
-    time_ns:int64 ->
-    tid:int ->
-    params:extension_parameter list ->
-    data:(string * Trace_core.user_data) list ->
-    name:string ->
-    float ->
-    unit;
-      (** Emit the current value of a counter *)
-  on_extension_event: 'st -> time_ns:int64 -> tid:int -> extension_event -> unit;
-      (** Extension event
-          @since 0.8 *)
-}
-(** Callbacks for a subscriber. There is one callback per event in {!Trace}. The
-    type ['st] is the state that is passed to every single callback. *)
-
-(** Dummy callbacks. It can be useful to reuse some of these functions in a real
-    subscriber that doesn't want to handle {b all} events, but only some of
-    them.
-
-    To write a subscriber that only supports some callbacks, this can be handy:
-    {[
-      module My_callbacks = struct
-      type st = my_own_state
-      include Callbacks.Dummy
-      let on_counter (st:st) ~time_ns ~tid ~data ~name v : unit = ...
-      end
-    ]} *)
-module Dummy = struct
-  let on_init _ ~time_ns:_ = ()
-  let new_span_id _ = Int64.min_int
-  let new_trace_id _ = -1L
-  let on_shutdown _ ~time_ns:_ = ()
-  let on_message _ ~time_ns:_ ~tid:_ ~span:_ ~params:_ ~data:_ _msg = ()
-  let on_counter _ ~time_ns:_ ~tid:_ ~params:_ ~data:_ ~name:_ _v = ()
-  let on_enter_span _ _sp = ()
-  let on_exit_span _ ~time_ns:_ ~tid:_ _ = ()
-  let on_extension_event _ ~time_ns:_ ~tid:_ _ = ()
-end
-
-(** Build a set of callbacks.
-    @since NEXT_RELEASE *)
-let make ~new_span_id ?(new_trace_id = Dummy.new_trace_id)
-    ?(on_init = Dummy.on_init) ?(on_enter_span = Dummy.on_enter_span)
-    ?(on_exit_span = Dummy.on_exit_span) ?(on_message = Dummy.on_message)
-    ?(on_counter = Dummy.on_counter)
-    ?(on_extension_event = Dummy.on_extension_event)
-    ?(on_shutdown = Dummy.on_shutdown) () : _ t =
-  {
-    on_init;
-    new_span_id;
-    new_trace_id;
-    on_enter_span;
-    on_exit_span;
-    on_message;
-    on_counter;
-    on_extension_event;
-    on_shutdown;
-  }
-
-(** Dummy callbacks, ignores all events. *)
-let dummy () : _ t = make ~new_span_id:(fun () -> Span_sub.dummy_span_id) ()
diff --git a/src/subscriber/subscriber.ml b/src/subscriber/subscriber.ml
deleted file mode 100644
index 1b48fbd..0000000
--- a/src/subscriber/subscriber.ml
+++ /dev/null
@@ -1,99 +0,0 @@
-(** Trace subscribers *)
-
-(** A trace subscriber. It pairs a set of callbacks with the state they need
-    (which can contain a file handle, a socket to write events to, config,
-    etc.).
-
-    The design goal for this is that it should be possible to avoid allocations
-    whenever the trace collector invokes the callbacks. *)
-type t =
-  | Sub : {
-      st: 'st;
-      callbacks: 'st Callbacks.t;
-    }
-      -> t
-
-(** Dummy subscriber that ignores every call. *)
-let dummy : t = Sub { st = (); callbacks = Callbacks.dummy () }
-
-open struct
-  type st = t array
-
-  let new_span_id (st : st) =
-    let (Sub { st; callbacks = cb }) = Array.get st 0 in
-    cb.new_span_id st
-
-  let new_trace_id st =
-    let (Sub { st; callbacks = cb }) = Array.get st 0 in
-    cb.new_trace_id st
-
-  let on_init st ~time_ns =
-    for i = 0 to Array.length st - 1 do
-      let (Sub { st; callbacks = cb }) = Array.get st i in
-      cb.on_init st ~time_ns
-    done
-
-  let on_shutdown st ~time_ns =
-    for i = 0 to Array.length st - 1 do
-      let (Sub { st; callbacks = cb }) = Array.get st i in
-      cb.on_shutdown st ~time_ns
-    done
-
-  let on_enter_span st span =
-    for i = 0 to Array.length st - 1 do
-      let (Sub { st; callbacks = cb }) = Array.get st i in
-      cb.on_enter_span st span
-    done
-
-  let on_exit_span st ~time_ns ~tid span =
-    for i = 0 to Array.length st - 1 do
-      let (Sub { st; callbacks = cb }) = Array.get st i in
-      cb.on_exit_span st ~time_ns ~tid span
-    done
-
-  let on_message st ~time_ns ~tid ~span ~params ~data msg =
-    for i = 0 to Array.length st - 1 do
-      let (Sub { st; callbacks = cb }) = Array.get st i in
-      cb.on_message st ~time_ns ~tid ~span ~params ~data msg
-    done
-
-  let on_counter st ~time_ns ~tid ~params ~data ~name n =
-    for i = 0 to Array.length st - 1 do
-      let (Sub { st; callbacks = cb }) = Array.get st i in
-      cb.on_counter st ~time_ns ~tid ~params ~data ~name n
-    done
-
-  let on_extension_event st ~time_ns ~tid ev : unit =
-    for i = 0 to Array.length st - 1 do
-      let (Sub { st; callbacks = cb }) = Array.get st i in
-      cb.on_extension_event st ~time_ns ~tid ev
-    done
-
-  let tee_cb : t array Callbacks.t =
-    {
-      Callbacks.on_init;
-      new_span_id;
-      new_trace_id;
-      on_enter_span;
-      on_exit_span;
-      on_message;
-      on_counter;
-      on_extension_event;
-      on_shutdown;
-    }
-end
-
-(** Tee multiple subscribers, ie return a subscriber that forwards to every
-    subscriber in [subs].
-
-    To generate a new span or trace ID, the first subscriber of the list is
-    used. *)
-let tee_l (subs : t list) : t =
-  match subs with
-  | [] -> dummy
-  | [ s ] -> s
-  | l -> Sub { st = Array.of_list l; callbacks = tee_cb }
-
-(** [tee s1 s2] is a subscriber that forwards every call to [s1] and [s2] both.
-*)
-let tee (s1 : t) (s2 : t) : t = tee_l [ s1; s2 ]
diff --git a/src/subscriber/trace_subscriber.ml b/src/subscriber/trace_subscriber.ml
deleted file mode 100644
index e6113bc..0000000
--- a/src/subscriber/trace_subscriber.ml
+++ /dev/null
@@ -1,130 +0,0 @@
-open Trace_core
-
-type t = Collector.t
-
-module Private_ = struct
-  let mock = ref false
-  let get_now_ns_ = ref Time_.get_time_ns
-  let get_tid_ = ref Thread_.get_tid
-
-  (** Now, in nanoseconds *)
-  let[@inline] now_ns () : int64 =
-    if !mock then
-      !get_now_ns_ ()
-    else
-      Time_.get_time_ns ()
-
-  let[@inline] tid_ () : int =
-    if !mock then
-      !get_tid_ ()
-    else
-      Thread_.get_tid ()
-end
-
-open struct
-  module A = Trace_core.Internal_.Atomic_
-  open Private_
-
-  type Trace_core.span += Span_sub of Span_sub.t
-
-  let enter_span (Subscriber.Sub { st; callbacks = cb }) ~__FUNCTION__ ~__FILE__
-      ~__LINE__ ~params ~data ~parent name : span =
-    let id = cb.new_span_id st in
-    let tid = tid_ () in
-    let time_ns = now_ns () in
-
-    let trace_id =
-      match parent with
-      | P_some (Span_sub span) -> span.trace_id
-      | _ -> cb.new_trace_id st
-    in
-
-    let flavor = ref `Sync in
-    List.iter
-      (function
-        | Core_ext.Extension_span_flavor f -> flavor := f
-        | _ -> ())
-      params;
-
-    let span : Span_sub.t =
-      {
-        name;
-        id;
-        tid;
-        __FUNCTION__;
-        __FILE__;
-        __LINE__;
-        data;
-        parent;
-        trace_id;
-        flavor = !flavor;
-        params;
-        time_ns;
-        time_exit_ns = Int64.max_int;
-      }
-    in
-
-    cb.on_enter_span st span;
-
-    Span_sub span
-
-  let exit_span (Subscriber.Sub { st; callbacks = cb }) span : unit =
-    match span with
-    | Span_sub span ->
-      let time_ns = now_ns () in
-      span.time_exit_ns <- time_ns;
-      let tid = tid_ () in
-      cb.on_exit_span st ~time_ns ~tid span
-    | _ -> ()
-
-  let add_data_to_span _sub span data =
-    match span with
-    | Span_sub span -> span.data <- List.rev_append data span.data
-    | _ -> ()
-
-  let message (Subscriber.Sub { st; callbacks = cb }) ~params ~data ~span msg :
-      unit =
-    let time_ns = now_ns () in
-    let tid = tid_ () in
-    let span =
-      match span with
-      | Some (Span_sub s) -> Some s
-      | _ -> None
-    in
-    cb.on_message st ~time_ns ~tid ~span ~params ~data msg
-
-  let counter_float (Subscriber.Sub { st; callbacks = cb }) ~params ~data name f
-      : unit =
-    let time_ns = now_ns () in
-    let tid = tid_ () in
-    cb.on_counter st ~tid ~time_ns ~params ~data ~name f
-
-  let[@inline] counter_int sub ~params ~data name i =
-    counter_float sub ~params ~data name (float_of_int i)
-
-  let init (Subscriber.Sub { st; callbacks = cb }) =
-    (* init code *)
-    let time_ns = now_ns () in
-    cb.on_init st ~time_ns
-
-  let shutdown (Subscriber.Sub { st; callbacks = cb }) =
-    let time_ns = now_ns () in
-    cb.on_shutdown st ~time_ns
-
-  let extension_event (Subscriber.Sub { st; callbacks = cb }) ev =
-    let tid = tid_ () in
-    let time_ns = now_ns () in
-    cb.on_extension_event st ~time_ns ~tid ev
-
-  (* TODO: do we want to track this? *)
-  let current_span _ = None
-
-  let coll_cbs : t Collector.Callbacks.t =
-    Collector.Callbacks.make ~enter_span ~exit_span ~current_span ~message
-      ~add_data_to_span ~counter_int ~counter_float ~extension:extension_event
-      ~init ~shutdown ()
-end
-
-(** A collector that calls the callbacks of subscriber *)
-let collector (self : Subscriber.t) : collector =
-  Collector.C_some (self, coll_cbs)
diff --git a/src/subscriber/trace_subscriber.mli b/src/subscriber/trace_subscriber.mli
deleted file mode 100644
index 945328a..0000000
--- a/src/subscriber/trace_subscriber.mli
+++ /dev/null
@@ -1,64 +0,0 @@
-(** Generic subscribers.
-
-    This defines the notion of a {b subscriber}, a set of callbacks for every
-    trace event. It also defines a collector that needs to be installed for the
-    subscriber(s) to be called.
-
-    Thanks to {!Subscriber.tee_l} it's possible to combine multiple subscribers
-    into a single collector.
-
-    @since 0.8 *)
-
-module Callbacks = Callbacks
-module Subscriber = Subscriber
-module Span_sub = Span_sub
-
-(** {2 Main API} *)
-
-type t = Subscriber.t
-(** A trace subscriber. It pairs a set of callbacks with the state they need
-    (which can contain a file handle, a socket to write events to, config,
-    etc.).
-
-    The design goal for this is that it should be possible to avoid allocations
-    whenever the trace collector invokes the callbacks. *)
-
-val collector : t -> Trace_core.collector
-(** A collector that calls the subscriber's callbacks. It uses [mtime] (if
-    available) to obtain timestamps. *)
-
-(** A counter-based span generator.
-    @since NEXT_RELEASE *)
-module Span_id_generator : sig
-  type t
-
-  val create : unit -> t
-  val gen : t -> Span_sub.span_id
-end
-
-(** A counter-based generator.
-    @since NEXT_RELEASE *)
-module Trace_id_generator : sig
-  type t
-
-  val create : unit -> t
-  val gen : t -> Span_sub.trace_id
-end
-
-(**/**)
-
-module Private_ : sig
-  val mock : bool ref
-  (** Global mock flag. If enable, all timestamps, tid, etc should be faked. *)
-
-  val get_now_ns_ : (unit -> int64) ref
-  (** The callback used to get the current timestamp *)
-
-  val get_tid_ : (unit -> int) ref
-  (** The callback used to get the current thread's id *)
-
-  val now_ns : unit -> int64
-  (** Get the current timestamp, or a mock version *)
-end
-
-(**/**)