Blizzard has given us our first tease of the upcoming 24th Overwatch hero: a blog post spotlighting Efi Oladele, an 11-year-old robotics prodigy from Numbani and the recipient of "the Adawe Foundation's prestigious 'genius grant.'"
The blog post is an in-universe interview with Oladele discussing her achievements in robotics and artificial intelligence. Similar blog posts were made before previous character announcements, such as during the Sombra ARG.
This information backs up a statement made by game director Jeff Kaplan that suggested the 24th Overwatch hero would not be Doomfist, as many people had speculated. It's unclear if Oladele herself will be the 24th hero, or if she simply has something to do with the upcoming character's lore and backstory.
Considering it's unlikely Blizzard will have an 11-year-old trotting into battle herself, current speculation points to the 24th hero either being a grown-up version of Oladele, or (considering her talent with AI) one of her robotic creations. However, a Twitter post from Overwatch lead writer Michael Chu says that the in-universe interview takes place in the present day of the Overwatch timeline, thus ruling out the theory that we might see a grown-up Oladele on the battlefield.
Looks like we'll find out more in the coming days.