We do not impose a hard cap on MAUs. We'll never halt access or send you a weird bill based on overages. We allow for variance as we know a company's user base can grow unexpectedly over time. That said, we do limit the amount of users that will be saved in your dashboard.
When you exceed your MAU, your new users and changes to existing users (such as new attributes) will no longer appear in the dashboard. It's important to note that your users will continue to evaluate their flags correctly. This only impacts your ability to view user updates in the dashboard.