A standalone reboot utility showed up in 4.0BSD.

In AT&T UNIX init has a case for reboot and is present in the version shipped
with V5.
http://minnie.tuhs.org/cgi-bin/utree.pl?file=V5/usr/source/s1/init.c

Amend HISTORY section.
Bump date.

sbin/reboot/reboot.8

@@ -1,4 +1,4 @@
-.\"	$NetBSD: reboot.8,v 1.29 2011/02/16 19:32:26 wiz Exp $
+.\"	$NetBSD: reboot.8,v 1.30 2016/09/12 05:43:15 sevan Exp $
 .\"
 .\" Copyright (c) 1990, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -29,7 +29,7 @@
 .\"
 .\"	@(#)reboot.8	8.1 (Berkeley) 6/9/93
 .\"
-.Dd February 16, 2011
+.Dd September 12, 2016
 .Dt REBOOT 8
 .Os
 .Sh NAME
@@ -133,7 +133,7 @@ users advance warning of their impending doom.
 A
 .Nm
 command appeared in
-.At v6 .
+.Bx 4.0 .
 .Pp
 The
 .Nm poweroff