It looks like Population Zero is giving away 5000 total copies of the full game.
Additionally, these keys provide access to all future betas as well, with the next round starting March 21. The giveaway is hosted on Gleam, with the press release citing the ongoing fight against Coronavirus as the impetus,
“We hope to encourage more video game developers and companies to join us in the battle against COVID-19 with Hadoukens, BFGs, magic spells, and superpowers.
Spread the word with #GamesVersusVirus hashtag! Be mindful of your health and the health of others.”
These keys are given away at random as you complete certain tasks listed at the Gleam site linked above. You must redeem them on PZOnline.com. One final note, if upon receiving the key, you redeem a “Pioneer Package,” you have the full game and are all set.