https://www.tuhs.org/cgi-bin/utree.pl?file=4BSD/usr/src/cmd/reboot.c
not in 3BSD
https://www.tuhs.org/cgi-bin/utree.pl?file=3BSD/usr/src/cmd

Index: sbin/reboot/reboot.8
===================================================================
RCS file: /cvs/src/sbin/reboot/reboot.8,v
diff -u -p -r1.50 reboot.8
--- sbin/reboot/reboot.8	3 Sep 2016 14:25:05 -0000	1.50
+++ sbin/reboot/reboot.8	18 Dec 2024 09:24:31 -0000
@@ -107,4 +107,4 @@ users advance warning of their impending
 A
 .Nm reboot
 command appeared in
-.At v6 .
+.Bx 4.0 .