The validator set is now entirely permissionless on testnet. There is a self-delegation requirement of 10k HYPE to register a new validator, and the existing validators must self-delegate this much in order to be eligible for the active set. The top N validators by total delegated stake form the active set.
Currently N=50 on testnet. The existing validators each received 10k testnet HYPE in their validator wallets to self-delegate.