I have not received an official Halo Waypoint notification yet but I received an email several hours ago;
We’re excited to invite you to multiplayer tech previews for Halo Infinite this weekend and next! During this weekend, September 23-26, our goals will be to receive feedback on Arena, Training Mode, as well as the new Halo Waypoint web and app experiences. Next weekend, September 30 - October 3, Big Team Battle will go live and take it up a notch.
On Sunday, October 3, we will be sending out a survey to a portion of Halo Insiders to collect feedback on the flight. Please keep an eye out for it, as it’s valuable to get your thoughts and feedback while everything is still fresh in your mind.
Please head to Halo Waypoint, click on your most recent flight, and read up on how to download your pre-release build.
I downloaded the ‘Xbox Insider’ app and then the ‘Halo Infinite Flight Preview’. It first said I was unauthorised to access the Flight, but after a Hard Reset, I was able to access the Flight Preview.
There is still Hope my fellow Spartans!