Debian 10 (Buster) was released two hours ago. \o/
When using ‘apt-get update’, I can see the message:
E: Repository 'http://security.debian.org/debian-security buster/updates InRelease' changed its 'Suite' value from 'testing' to 'stable' N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.
# apt-get --allow-releaseinfo-change update