Before Alex Garland made the transition to film directing, he was a writer. One of his earliest efforts was the novel that became the basis of the Leonardo DiCaprio movie The Beach. After writing a couple books, Garland moved on to writing movies before directing them, such as his most recent film Annihilation. Recently, Garland was asked if he might ever consider taking a shot at adapting The Beach himself, the writer/director's response was nebulous but interesting. In Garland's words...
Alex Garland revealed the news that somebody is apparently working on another adaptation of The Beach, but he doesn't reveal anything beyond the fact that he finds them to be talented. So, is somebody else working on a script or he is working a script? With the fact that this project has never been officially announced, Garland would need to be cagey about any response that he gave, the studio wouldn't like it if he spilled the beans about the project before they were ready. Also, Garland calls it a "possible" adaptation, which means it like;y hasn't been given the green light, all the more reason he can't say anything.
With Alex Garland now committed to moviemaking fulltime, something else he confirms during the same Reddit AMA where he revealed The Beach news, it would make all the sense that if a studio was interested in remaking The Beach, it would call Alex Garland. Why would you call anybody else? There's really no argument to be made that Garland isn't talented, though he could be making a bit of a joke by pointing that out himself. Fans of the novel would probably like to see the writer of the book tackle it on the big screen.
Of course, if we take Alex Garland at his word, it could be that somebody else, who Garland legitimately believes is a talented writer, is currently working on the script, as the writer of the novel, Garland would be in the loop anyway, as the studio likely needed to work with him on the rights. The next best thing to a Garland written adaptation would be a Garland endorsed adaptation. It's barely possible that Garland could even be referring to the television adaptation that was reported several years ago, but that project is so old it's impossible to know if it's still active.
The original The Beach screenplay was written by John Hodge who wrote the screenplay for Trainspotting and it was directed by Danny Boyle who also directed Garland's own 28 Days Later. It wasn't well loved by critics, though the fact that it starred a post-Titanic DiCaprio made it a financial success.
One way or another, something related to The Beach is currently in development. We'll have to wait and see what it is.