Locke & Key creators Gabriel Rodriguez and Joe Hill are both attached to the crossover, along with Locke & Key colorist Jay Fotos and editor Chris Ryall. The crossover is a collaboration between IDW Publishing, the publisher behind Locke & Key, and DC Comics, the publisher responsible for The Sandman Universe titles (the original Sandman series was published by now-defunct DC Comics imprint Vertigo Comics).

IDW announced the crossover on Twitter, along with a brief video featuring the key to Hell from Sandman: Season of Mists by Neil Gaiman, Kelley Jones, Malcolm Jones III, Dan Vozzo, and Todd Klein (a nice catch by Beat reader Donnie in the comment section).
https://www.comicsbeat.com/locke-key-sandman-crossover/