@abcdw Hm since there was no reaction in IRC, I wanted to send it to mailing list. But I cannot reproduce it:

(use-modules (ice-9 threads))
(let ((th (call-with-new-thread (lambda () 'hi))))
(pk (join-thread th))
(pk (thread-exited? th))
(sleep 1)
(pk (thread-exited? th)))

gives me:

$ guile /tmp/x.scm

;;; (hi)

;;; (#t)

;;; (#t)

I am on guile 3.0.9.