Re:Zero revealed big news right after the final episode of Season 3 aired. The official channels announced that Re:Zero Season 4 is now in production. Along with the announcement, they also shared a teaser video, a key visual, and a special illustration from the light novel artist Shinichiro Otsuka.
Did you think we’d have to wait another four years? We won’t keep you waiting! So, the fourth season has been decided! There’s that girl we remember, Subaru isn’t wearing a jersey, there’s an enemy, Julius has a sad look on his face, and just looking at the teaser visuals evokes all kinds of emotions. What kind of scenery will the next season show us? Look forward to the broadcast!
Yusuke Kobayashi

While there is no official release date, it’s expected that Season 4 will take a while, possibly releasing around 2027. This season will adapt The Corridor of Memories, covering Volume 21 of the light novel.
The ReZero: Starting Life in Another World light novel series is written by Tappei Nagatsuki and illustrated by Shinichiro Otsuka. It was first published as a web novel in 2012 before being serialized under MF Bunko J in 2014. The series was later adapted into an anime by White Fox, with the first season airing in April 2016. Crunchyroll describes the story as:
Natsuki Subaru, an ordinary high school student, is on his way home from the convenience store when he finds himself transported to another world. As he’s lost and confused in a new world where he doesn’t even know left from right, the only person to reach out to him was a beautiful girl with silver hair. Determined to repay her somehow for saving him from his own despair, Subaru agrees to help the girl find something she’s looking for…
Source: Crunchyroll