Here is the CompTIA Linux+ XK0-004 Beta Exam announcement thread on Reddit:
https://www.reddit.com/r/CompTIA/comments/907c3m/linux_xk0004_announcement_thread
I signed up to take the beta exam on October 12.
I am taking the Linux+ LX0-104 exam on September 29, but I figured that for only $50, I should give the beta exam a shot.
If you want the "two-for-one" certification deal (a cert from CompTIA and a cert from LPI), take the current LX0-103/LX0-104 exams before they are retired sometime next year!