Faux-launched in May and rolled out to all iOS users in October, Instant Articles is Facebook's bid to capture more of your attention by directly hosting articles and blog posts published elsewhere on the web. That way, when a FB user clicks a link to one of these articles, they open instantly inside the Facebook app (hence the name).
The articles are shown to users with a minimum of adverts and tracking detritus (although Facebook does have an InstantAds to match the Instant Articles). Publishers can sell adverts against their articles, and collect 100% of the revenues, or let FB sell adverts and collect 70% of the proceeds.
The program launched with only a handful of publishers, but today FB says that more than 350 publishers around the world have joined the Instant Articles program to date, with more joining everyday.
Not all publishers are happy with the ad revenues they've been earning from this program, so this last part is still being tweaked to satisfy publishers while keeping users happy.