Niantic
The first wave of Deoxys EX Raid Passes have begun appearing in Pokemon Go.
Players have been reporting receiving EX Raid Passes on The Silph Road Subreddit since around Thursday. Our own reporter received a pass for an EX Raid on October 1. Others like user cmdb17 have reported receiving invitations to EX Raids on October 2.
Be aware that there is a glitch regarding EX Raids appearing to be cancelled, as user Laughing_cucumber illustrates. Niantic is working on a fix according to their Niantic Support Twitter account.
Niantic promised that EX Raid Passes would be sent out in the next wave after they announced the Pokemon on September 19. They also announced updates to how EX Raids work. You can now see which Gyms are eligible to host an EX Raid via a tag in the Gym details. You can also invite one Ultra Friend or Best Friend to join you in the EX Raid.
To get an EX Raid Pass, you need to complete at least one Raid at an EX Raid eligible Gym within the past few weeks, according to Pokemon Go Hub. To increase your chances of getting a pass, you can get a high-level Gym Badge at the EX Raid eligible Gym and complete 100 Raids to get the silver ranking of the Champion badge, according to the publication.