Domain beta-wallet.trezor.io originally hosted beta build of mytrezor wallet. With initial release of Trezor Suite this domain was decided to become entry point of closed beta program for Trezor Suite.
It has special structure:
Stable version (currently in public beta) is hosted on suite.trezor.io and should go live on 14th October 2020 via soft launch. Check fancy diagram how it's going to work in it's entirety.
Each of the above mentioned environments have its own staging environment counterpart.
Staging environments are only accessible within SatoshiLabs internal IP range (office + VPN).