"I'm a survivor," sang Destiny's Child in 2001; thus proving once and for all that three people are better at tackling a harsh wilderness (and/or shitty boyfriends) than one. In recognition of that, Klei has given all owners of their survival game Don't Starve a free copy of standalone multiplayer expansion Don't Starve Together.
The multiplayer component was always due to be given, for free, to Don't Starve owners on completion of its time in Early Access. Despite this, Don't Starve Together is not yet out of beta. Klei has decided to hand it out nonetheless. If you owned Don't Starve prior to June 3, you now own Don't Starve Together, too.
"Today, we welcome 2 million new players into the Don't Starve Together community," writes Klei. "Thank you once again to everyone who supported us on this journey."
As for future buyers of Don't Starve, you won't receive a copy of the expandalone. Instead, Klei has released a Don't Starve Mega Pack, featuring both games, and an extra giftable copy of Don't Starve Together, for 17/$20.
If you're eligible for a copy but don't know where it is, head over to Klei's FAQ page.