How do streaks work?
As long as you do at least one session per working day, your streak will continue. By default working days are Monday through Friday but you can configure that in your account settings.
Once you reach a 30+ streak, you start collecting Streak Flames! These are collectable and show up on your account. You never lose a Streak Flame once collected, but if you break your streak, you need to build up to 30+ again before collecting any more.
You can read more about it in the blog post: New streak system