Last night and earlier today, Apple rolled out two changes to TestFlight they first announced at WWDC: developers can now invite up to 2,000 testers to their betas, which now expire after 60 days instead of 30.
From Apple's developer blog:
Now you can invite up to 2,000 users to beta test your iOS and tvOS apps before you release them on the App Store. TestFlight makes it simple to invite testers using just their email address and lets testers easily provide valuable feedback within the TestFlight app.
As someone who's been affected by expired TestFlight betas too many times in the past, the expiration date change is especially welcome.