...they're just grays :)
(require :gray-streams) (subtypep 'gray-streams:fundamental-stream 'stream) ;; => NIL, T
This doesn't matter for flexi-streams and other libs, but cl-store has a few DECLAREs. I don't know exactly when a type declaration is an assertion in ABCL, but at least it is for a stream with nonzero safety.
Best, lmj