Good for you.
Whether or not he keeps it up I am happy for him and I'm sure it's exciting for you. Too often I think we get to focusing on thoughts like "well he might relapse". He might... I might get hit by lightning, you might hit the lotto... But since none of those three things happened today, congratulations and I'm happy for you. Just because you are aware that you need time and consistency to trust the good start doesn't mean you can't smile and sleep well tonight focusing on the good things that happened today.
Ps... If you do hit the lotto remember your buddies lol