sys/netinet6/in6_ifattach.c r1.114 limited it to SLAAC addresses in 2019.
#!/bin/sh -
#
-# $OpenBSD: netstart,v 1.223 2022/10/31 19:25:16 kn Exp $
+# $OpenBSD: netstart,v 1.224 2022/10/31 19:48:50 kn Exp $
# Turn off Strict Bourne shell mode.
set +o sh
fi
# Load key material for the generation of IPv6 Semantically Opaque Interface
-# Identifiers (SOII) used for link local and SLAAC addresses.
+# Identifiers (SOII) used for SLAAC addresses.
$PRINT_ONLY || [[ ! -f /etc/soii.key ]] ||
sysctl -q "net.inet6.ip6.soiikey=$(</etc/soii.key)"