Definition
ExpressVPN introduced Lightway as an alternative to OpenVPN and IKEv2 in its apps and later published the core code as open source. It is not a version of WireGuard: it uses wolfSSL, a compact TLS library, for its cryptography, and it can run over UDP or TCP.
How it works
Like WireGuard, Lightway keeps its codebase small so it is easier to audit. It aims to connect in a fraction of a second and to resume quickly when a phone switches between Wi-Fi and mobile data. ExpressVPN has commissioned third-party security reviews of the protocol, and has added post-quantum key exchange to it.
Why it matters
If you use ExpressVPN, Lightway is usually the default and the protocol most people should keep. Because it exists only inside ExpressVPN's apps, you cannot use it with a different provider or a generic client, which is the main trade-off against WireGuard and OpenVPN.