diff --git a/src/client/batch.ml b/src/client/batch.ml
index 1fc4aaa9..d26cb04f 100644
--- a/src/client/batch.ml
+++ b/src/client/batch.ml
@@ -1,4 +1,4 @@
-module Otel = Opentelemetry
+open Opentelemetry_util
 
 type 'a t = {
   mutable size: int;
@@ -47,7 +47,7 @@ let ready_to_pop ~force ~now self =
 
 let pop_if_ready ?(force = false) ~now (self : _ t) : _ list option =
   let rev_batch_opt =
-    Otel.Util_mutex.protect self.mutex @@ fun () ->
+    Util_mutex.protect self.mutex @@ fun () ->
     if ready_to_pop ~force ~now self then (
       assert (self.q <> []);
       let batch = self.q in
@@ -72,7 +72,7 @@ let rec push_unprotected (self : _ t) ~(elems : _ list) : unit =
     push_unprotected self ~elems:xs
 
 let push (self : _ t) elems : [ `Dropped | `Ok ] =
-  Otel.Util_mutex.protect self.mutex @@ fun () ->
+  Util_mutex.protect self.mutex @@ fun () ->
   if self.size >= self.high_watermark then
     (* drop this to prevent queue from growing too fast *)
     `Dropped
diff --git a/src/client/self_trace.ml b/src/client/self_trace.ml
index 28baaf5d..23dd258b 100644
--- a/src/client/self_trace.ml
+++ b/src/client/self_trace.ml
@@ -1,21 +1,21 @@
-module OT = Opentelemetry
+open Common_
 
 let enabled = Atomic.make false
 
-let[@inline] add_event (scope : OT.Span.t) ev = OT.Span.add_event scope ev
+let[@inline] add_event (scope : OTEL.Span.t) ev = OTEL.Span.add_event scope ev
 
-let dummy_trace_id_ = OT.Trace_id.dummy
+let dummy_trace_id_ = OTEL.Trace_id.dummy
 
-let dummy_span_id = OT.Span_id.dummy
+let dummy_span_id = OTEL.Span_id.dummy
 
 (* FIXME: get an explicit tracer instead *)
 let with_ ?kind ?attrs name f =
   if Atomic.get enabled then
-    OT.Tracer.with_ ?kind ?attrs name f
+    OTEL.Tracer.with_ ?kind ?attrs name f
   else (
     (* A new scope is needed here because it might be modified *)
-    let span : OT.Span.t =
-      OT.Span.make ~trace_id:dummy_trace_id_ ~id:dummy_span_id ~start_time:0L
+    let span : OTEL.Span.t =
+      OTEL.Span.make ~trace_id:dummy_trace_id_ ~id:dummy_span_id ~start_time:0L
         ~end_time:0L name
     in
     f span
diff --git a/src/client/self_trace.mli b/src/client/self_trace.mli
index 26e7b3e9..b6b371ef 100644
--- a/src/client/self_trace.mli
+++ b/src/client/self_trace.mli
@@ -1,12 +1,14 @@
 (** Mini tracing module (disabled if [config.self_trace=false]) *)
 
-val add_event : Opentelemetry.Span.t -> Opentelemetry.Event.t -> unit
+open Common_
+
+val add_event : OTEL.Span.t -> OTEL.Event.t -> unit
 
 val with_ :
-  ?kind:Opentelemetry.Span_kind.t ->
-  ?attrs:(string * Opentelemetry.value) list ->
+  ?kind:OTEL.Span_kind.t ->
+  ?attrs:(string * OTEL.value) list ->
   string ->
-  (Opentelemetry.Span.t -> 'a) ->
+  (OTEL.Span.t -> 'a) ->
   'a
 
 val set_enabled : bool -> unit
diff --git a/src/client/stdout_exporter.ml b/src/client/stdout_exporter.ml
index 05122369..71c8e2d1 100644
--- a/src/client/stdout_exporter.ml
+++ b/src/client/stdout_exporter.ml
@@ -1,10 +1,11 @@
 (** A simple exporter that prints on stdout *)
 
 open Common_
-open OTEL
+open Opentelemetry_util
 
 open struct
-  let pp_span out (sp : Span.t) =
+  let pp_span out (sp : OTEL.Span.t) =
+    let open OTEL in
     Format.fprintf out
       "@[<2>SPAN@ trace_id: %a@ span_id: %a@ name: %S@ start: %a@ end: %a@]@."
       Trace_id.pp
diff --git a/src/client/sync_queue.ml b/src/client/sync_queue.ml
index 10983b2f..46d46af1 100644
--- a/src/client/sync_queue.ml
+++ b/src/client/sync_queue.ml
@@ -1,4 +1,4 @@
-module UM = Opentelemetry.Util_mutex
+module UM = Opentelemetry_util.Util_mutex
 
 type 'a t = {
   mutex: Mutex.t;
diff --git a/src/core/common_.ml b/src/core/common_.ml
index 30bb39d2..c6544d5d 100644
--- a/src/core/common_.ml
+++ b/src/core/common_.ml
@@ -2,4 +2,3 @@ let spf = Printf.sprintf
 
 module Proto = Opentelemetry_proto
 module Atomic = Opentelemetry_atomic.Atomic
-module Ambient_context = Opentelemetry_ambient_context
diff --git a/src/core/dune b/src/core/dune
index debbd5c0..dce03edd 100644
--- a/src/core/dune
+++ b/src/core/dune
@@ -1,15 +1,14 @@
 (library
- (name opentelemetry)
- (synopsis "API for opentelemetry instrumentation")
+ (name opentelemetry_core)
+ (public_name opentelemetry.core)
+ (synopsis "Core types and definitions for opentelemetry")
  (flags :standard -warn-error -a+8 -open Opentelemetry_util)
  (libraries
   opentelemetry.proto
   opentelemetry.util
-  opentelemetry.ambient-context
   ptime
   ptime.clock.os
   pbrt
   threads
   opentelemetry.atomic
-  hmap)
- (public_name opentelemetry))
+  hmap))
diff --git a/src/core/gc_metrics.ml b/src/core/gc_metrics.ml
index e565eb86..9e3c17cf 100644
--- a/src/core/gc_metrics.ml
+++ b/src/core/gc_metrics.ml
@@ -1,7 +1,7 @@
 open Common_
 
 open struct
-  let[@inline] bytes_per_word = Sys.word_size / 8
+  let bytes_per_word = Sys.word_size / 8
 
   let[@inline] word_to_bytes n = n * bytes_per_word
 
diff --git a/src/core/globals.ml b/src/core/globals.ml
index 36e3e975..0e5ccfb6 100644
--- a/src/core/globals.ml
+++ b/src/core/globals.ml
@@ -40,9 +40,10 @@ let add_global_attribute (key : string) (v : Value.t) : unit =
 
 (* add global attributes to this list *)
 let merge_global_attributes_ into : _ list =
-  let open Key_value in
-  let not_redundant kv = List.for_all (fun kv' -> kv.key <> kv'.key) into in
-  List.rev_append (List.filter not_redundant !global_attributes) into
+  let not_redundant kv =
+    List.for_all Key_value.(fun kv' -> kv.key <> kv'.key) into
+  in
+  List.rev_append Key_value.(List.filter not_redundant !global_attributes) into
 
 (** Default span kind in {!Span.create}. This will be used in all spans that do
     not specify [~kind] explicitly; it is set to "internal", following
diff --git a/src/core/span.ml b/src/core/span.ml
index 5b771d58..c4c0c8cd 100644
--- a/src/core/span.ml
+++ b/src/core/span.ml
@@ -123,11 +123,3 @@ let set_status = span_set_status
 let set_kind = span_set_kind
 
 let k_context : t Context.key = Context.new_key ()
-
-(** Find current span from ambient-context *)
-let get_ambient () : t option = Ambient_context.get k_context
-
-(** [with_ambient span f] runs [f()] with the current ambient span being set to
-    [span] *)
-let[@inline] with_ambient (span : t) (f : unit -> 'a) : 'a =
-  Ambient_context.with_key_bound_to k_context span (fun _ -> f ())
diff --git a/src/core/span.mli b/src/core/span.mli
index 138d60e1..34a4e858 100644
--- a/src/core/span.mli
+++ b/src/core/span.mli
@@ -108,9 +108,4 @@ val set_kind : t -> Span_kind.t -> unit
 (** Set the span's kind.
     @since 0.11 *)
 
-val get_ambient : unit -> t option
-(** Find current span from ambient-context *)
-
-val with_ambient : t -> (unit -> 'a) -> 'a
-(** [with_ambient span f] runs [f()] with the current ambient span being set to
-    [span] *)
+val k_context : t Context.key
diff --git a/src/core/span_id.ml b/src/core/span_id.ml
index bf9e7731..f7d926fc 100644
--- a/src/core/span_id.ml
+++ b/src/core/span_id.ml
@@ -1,5 +1,3 @@
-open Common_
-
 type t = bytes
 
 let[@inline] to_bytes self = self
@@ -13,7 +11,13 @@ let create () : t =
   Bytes.set b 0 (Char.unsafe_chr (Char.code (Bytes.get b 0) lor 1));
   b
 
-let is_valid = Util_bytes_.bytes_non_zero
+let[@inline] is_zero (self : t) : bool =
+  (* try to reduce branches *)
+  assert (Bytes.length self = 8);
+  let n1 = Bytes.get_int64_ne self 0 in
+  n1 = 0L
+
+let[@inline] is_valid self = not (is_zero self)
 
 let[@inline] of_bytes b =
   if Bytes.length b = 8 then
diff --git a/src/core/trace_id.ml b/src/core/trace_id.ml
index 8893a757..999eb3af 100644
--- a/src/core/trace_id.ml
+++ b/src/core/trace_id.ml
@@ -1,5 +1,3 @@
-open Common_
-
 type t = bytes
 
 let[@inline] to_bytes self = self
@@ -19,7 +17,14 @@ let[@inline] of_bytes b =
   else
     invalid_arg "trace ID must be 16 bytes in length"
 
-let is_valid = Util_bytes_.bytes_non_zero
+let[@inline] is_zero (self : t) : bool =
+  (* try to reduce branches *)
+  assert (Bytes.length self = 1);
+  let n1 = Bytes.get_int64_ne self 0 in
+  let n2 = Bytes.get_int64_ne self 8 in
+  n1 = 0L && n2 = 0L
+
+let[@inline] is_valid self = not (is_zero self)
 
 let to_hex = Util_bytes_.bytes_to_hex
 
diff --git a/src/lib/ambient_span.ml b/src/lib/ambient_span.ml
new file mode 100644
index 00000000..b8cc84e6
--- /dev/null
+++ b/src/lib/ambient_span.ml
@@ -0,0 +1,9 @@
+(** Find current span from ambient-context *)
+let[@inline] get () : Span.t option =
+  Opentelemetry_ambient_context.get Span.k_context
+
+(** [with_ambient span f] runs [f()] with the current ambient span being set to
+    [span] *)
+let[@inline] with_ambient (span : Span.t) (f : unit -> 'a) : 'a =
+  Opentelemetry_ambient_context.with_key_bound_to Span.k_context span (fun _ ->
+      f ())
diff --git a/src/lib/ambient_span.mli b/src/lib/ambient_span.mli
new file mode 100644
index 00000000..ecde51ea
--- /dev/null
+++ b/src/lib/ambient_span.mli
@@ -0,0 +1,6 @@
+val get : unit -> Span.t option
+(** Find current span from ambient-context *)
+
+val with_ambient : Span.t -> (unit -> 'a) -> 'a
+(** [with_ambient span f] runs [f()] with the current ambient span being set to
+    [span] *)
diff --git a/src/lib/dune b/src/lib/dune
new file mode 100644
index 00000000..4e68dbcb
--- /dev/null
+++ b/src/lib/dune
@@ -0,0 +1,25 @@
+(library
+ (name opentelemetry)
+ (public_name opentelemetry)
+ (synopsis "API for opentelemetry instrumentation")
+ (flags
+  :standard
+  -warn-error
+  -a+8
+  -open
+  Opentelemetry_util
+  -open
+  Opentelemetry_core
+  -open
+  Opentelemetry_core.Common_)
+ (libraries
+  opentelemetry.core
+  opentelemetry.proto
+  opentelemetry.util
+  opentelemetry.ambient-context
+  opentelemetry.atomic
+  ptime
+  ptime.clock.os
+  pbrt
+  threads
+  hmap))
diff --git a/src/core/logger.ml b/src/lib/logger.ml
similarity index 100%
rename from src/core/logger.ml
rename to src/lib/logger.ml
diff --git a/src/core/metrics_callbacks.ml b/src/lib/metrics_callbacks.ml
similarity index 100%
rename from src/core/metrics_callbacks.ml
rename to src/lib/metrics_callbacks.ml
diff --git a/src/core/metrics_callbacks.mli b/src/lib/metrics_callbacks.mli
similarity index 100%
rename from src/core/metrics_callbacks.mli
rename to src/lib/metrics_callbacks.mli
diff --git a/src/core/metrics_emitter.ml b/src/lib/metrics_emitter.ml
similarity index 100%
rename from src/core/metrics_emitter.ml
rename to src/lib/metrics_emitter.ml
diff --git a/src/core/opentelemetry.ml b/src/lib/opentelemetry.ml
similarity index 87%
rename from src/core/opentelemetry.ml
rename to src/lib/opentelemetry.ml
index 73e34600..8fe30707 100644
--- a/src/core/opentelemetry.ml
+++ b/src/lib/opentelemetry.ml
@@ -1,16 +1,12 @@
-(** Opentelemetry types and instrumentation *)
+(** Main Opentelemetry API for libraries and user code. *)
 
-module Rand_bytes = Rand_bytes
-(** Generation of random identifiers. *)
+module Core = Opentelemetry_core
+(** Core types and definitions *)
 
 module Alist = Alist
 (** Atomic list, for internal usage
     @since 0.7 *)
 
-module Util_mutex = Util_mutex
-(** Utilities for internal usage.
-    @since NEXT_RELEASE *)
-
 (** {2 Wire format} *)
 
 module Proto = Opentelemetry_proto
diff --git a/src/core/tracer.ml b/src/lib/tracer.ml
similarity index 97%
rename from src/core/tracer.ml
rename to src/lib/tracer.ml
index c7c81752..15ab1e97 100644
--- a/src/core/tracer.ml
+++ b/src/lib/tracer.ml
@@ -66,7 +66,7 @@ let with_thunk_and_finally ?(tracer = simple_main_exporter)
   let parent =
     match parent with
     | Some _ -> parent
-    | None -> Span.get_ambient ()
+    | None -> Ambient_span.get ()
   in
   let trace_id =
     match trace_id, parent with
@@ -109,7 +109,7 @@ let with_thunk_and_finally ?(tracer = simple_main_exporter)
 
     tracer#emit [ span ]
   in
-  let thunk () = Span.with_ambient span (fun () -> cb span) in
+  let thunk () = Ambient_span.with_ambient span (fun () -> cb span) in
   thunk, finally
 
 (** Sync span guard.