The new Memcached connector transparently replaces the old one shipped with 8.4 and offers the following improvements:

• support for both the TEXT and BINARY protocols (For both of these we have implemented authentication and encryption as well as autodetection which allow us to enable Memcached by default)
• authentication against the server security realms
• encryption (TLS)
• greatly improved performance
• protocol auto-detection which means the connector is enabled on the default server port out of the box

One caveat of the auto-detection is that for text protocol, clients must send a "fake" SET operation to authenticate on connection

if that is not possible for their applications, they should create a memcached connector on a dedicated port without authentication