From the source
Meta has launched an authenticated time service using NTS (Network Time Security, RFC 8915) at nts.meta.com, allowing devices to verify that time packets originated from Meta and were not tampered with.
The NTS servers are stateless, deriving cookie keys from a shared master secret rather than storing or replicating per-client state.
Meta has open-sourced the protocol, server, and client via its Time library on GitHub and is encouraging NTP client maintainers on Android and iOS to adopt NTS support.
