diff --git a/src/data/CCFun_vec.ml b/src/data/CCFun_vec.ml
index 220fce8d..539b1cd4 100644
--- a/src/data/CCFun_vec.ml
+++ b/src/data/CCFun_vec.ml
@@ -40,6 +40,10 @@ module Transient = struct
   exception Frozen
 end
 
+(* TODO: move transient from A.t to 'a t, as nodes can be owned by a transient,
+   not arrays.
+   Then do mutable push, and use it for append/filter/flatten/flat_map… *)
+
 (* function array *)
 module A = struct
   type 'a t = {
diff --git a/src/data/CCFun_vec.mli b/src/data/CCFun_vec.mli
index ad2a3d88..04c804fe 100644
--- a/src/data/CCFun_vec.mli
+++ b/src/data/CCFun_vec.mli
@@ -5,7 +5,7 @@
 (** Tree with a large branching factor for logarithmic operations with
     a low multiplicative factor.
 
-    {b status: unstable}
+    {b status: experimental. DO NOT USE (yet)}
 
     @since NEXT_RELEASE
 *)