Not on libbusybox.so: it's GPL, no API barrier, no stability promise.
diff --git a/Config.in b/Config.in
index 2048210..0afc34a 100644
--- a/Config.in
+++ b/Config.in
@@ -183,6 +183,11 @@
used by busybox itself. If you plan to write a separate
standalone application which uses libbusybox say 'Y'.
+ Note: libbusybox is GPL, not LGPL, and exports no stable API that
+ might act as a copyright barrier. We can and will modify the
+ exported function set between releases (even minor version number
+ changes), and happily break out-of-tree features.
+
Say 'N' if in doubt.
config CONFIG_FEATURE_SHARED_BUSYBOX