diff --git a/src/opentelemetry.ml b/src/opentelemetry.ml
index c65133b8..4ad36206 100644
--- a/src/opentelemetry.ml
+++ b/src/opentelemetry.ml
@@ -435,6 +435,7 @@ type value =
   [ `Int of int
   | `String of string
   | `Bool of bool
+  | `Float of float
   | `None
   ]
 
@@ -448,6 +449,7 @@ let _conv_value =
   | `Int i -> Some (Int_value (Int64.of_int i))
   | `String s -> Some (String_value s)
   | `Bool b -> Some (Bool_value b)
+  | `Float f -> Some (Double_value f)
   | `None -> None
 
 (**/**)
@@ -679,7 +681,7 @@ module Span : sig
   val id : t -> Span_id.t
 
   type key_value =
-    string * [ `Int of int | `String of string | `Bool of bool | `None ]
+    string * [ `Int of int | `String of string | `Bool of bool | `Float of float | `None ]
 
   val create :
     ?kind:kind ->
@@ -716,7 +718,7 @@ end = struct
     | Span_kind_consumer
 
   type key_value =
-    string * [ `Int of int | `String of string | `Bool of bool | `None ]
+    string * [ `Int of int | `String of string | `Bool of bool | `Float of float | `None ]
 
   type nonrec status_code = status_status_code =
     | Status_code_unset
diff --git a/src/trace/opentelemetry_trace.ml b/src/trace/opentelemetry_trace.ml
index 16990b73..b7a6162d 100644
--- a/src/trace/opentelemetry_trace.ml
+++ b/src/trace/opentelemetry_trace.ml
@@ -215,6 +215,19 @@ module Internal = struct
         let otel_span = exit_span' otrace_id sb in
         Otel.Trace.emit [ otel_span ]
 
+    let add_data_to_span otrace_id data =
+      let active_spans = Active_spans.get () in
+      match Active_span_tbl.find_opt active_spans.tbl otrace_id with
+      | None ->
+        (* FIXME: some kind of error/debug logging *)
+        ()
+      | Some sb ->
+        Active_span_tbl.replace active_spans.tbl otrace_id
+          { sb with data = sb.data @ data }
+
+    let add_data_to_manual_span Otrace.{ span = otrace_id; _ } data =
+      add_data_to_span otrace_id data
+
     let message ?span ~data:_ msg : unit =
       (* gather information from context *)
       let old_scope = Otel.Scope.get_ambient_scope () in
@@ -235,11 +248,11 @@ module Internal = struct
 
     let name_thread _name = ()
 
-    let counter_int name cur_val : unit =
+    let counter_int ~data:_ name cur_val : unit =
       let m = Otel.Metrics.(gauge ~name [ int cur_val ]) in
       Otel.Metrics.emit [ m ]
 
-    let counter_float name cur_val : unit =
+    let counter_float ~data:_ name cur_val : unit =
       let m = Otel.Metrics.(gauge ~name [ float cur_val ]) in
       Otel.Metrics.emit [ m ]
   end
diff --git a/src/trace/opentelemetry_trace.mli b/src/trace/opentelemetry_trace.mli
index 8d8e934d..fd3aa91b 100644
--- a/src/trace/opentelemetry_trace.mli
+++ b/src/trace/opentelemetry_trace.mli
@@ -126,6 +126,12 @@ module Internal : sig
 
         (See the notes at {!enter_manual_span} about {!Ambient_context}.) *)
 
+    val add_data_to_span :
+      Otrace.span -> (string * Otrace.user_data) list -> unit
+
+    val add_data_to_manual_span :
+      Otrace.explicit_span -> (string * Otrace.user_data) list -> unit
+
     val message :
       ?span:Otrace.span ->
       data:(string * Otrace.user_data) list ->
@@ -138,9 +144,11 @@ module Internal : sig
 
     val name_thread : string -> unit
 
-    val counter_int : string -> int -> unit
+    val counter_int :
+      data:(string * Otrace.user_data) list -> string -> int -> unit
 
-    val counter_float : string -> float -> unit
+    val counter_float :
+      data:(string * Otrace.user_data) list -> string -> float -> unit
   end
 
   type span_begin = {