So, those who haven't played through the above now free Half-Life games have at least six weeks to have some fun with the series.
The Half-Life games regularly go on sale, but if you've never played them before, now is the ideal time. Since they are all much older titles, it's unlikely your computer won't have the needed requirements to run them.
The offer is set to last until the day that Half-Life: Alyx launches which is sometime in March 2020.
Overnight, a number of Steam users got a curious notification: "Half-Life Collection now free-to-play until launch of Half-Life: Alyx!".
So, why is Valve being so generous? We're still waiting for an official Steam blog post or "collection" page to link to, but in the meantime, you can claim the limited-time offer at each game's individual Steam page (collected at this page for now). Valve are also throwing in ye olde expansion packs made by other studios, Half-Life: Opposing Force and Half-Life: Blue Shift, which tell events of the first game from new perspectives - maybe less relevant, but still nice if you want to get stuck in.
The Half-Life franchise is one of Valve's biggest contributions to the gaming industry next to Steam.
However, as they say, "Valve giveth and Valve taketh away", and boy oh boy does Valve plan on takething away. At the very least, it's probably worth playing through Half-Life 2 again so that Alyx, which is set before Gordon Freeman arrived in City 17, will make sense to you.
Sadly the wonderful (and definitely-in-the-Half-Life-universe) Portal and Portal 2 aren't included, but you can't have everything, eh?