“First published in 1982, B4: The Lost City was designed as a stand-alone adventure for use with the Dungeons and Dragons Basic Set. Author Tom Moldvay wrote the adventure with the intent of teaching novice gamemasters how to craft and run a dungeon. For that reason, many areas of the original adventure—including much of the titular city itself—are left undefined. And if you’ve read any of our earlier releases in the OAR series, you know that those areas are not going to be left blank for the Fifth Edition translation!I'm very happy with what Goodman Games did with B1-2 and X1. I'm looking forward to their treatment of S3 (Expedition to the Barrier Peaks) and am thrilled that B4 is now in the queue.
OAR #4: The Lost City will combine scans of the original edition of the module with 5E conversions and new material, as we’ve done with prior books in the OAR series. The conversion is being handled by Chris Doyle and Tim Wadzinski, the same team responsible for OAR #1: Into the Borderlands and OAR #2: The Isle of Dread.
At this time, the target release date is June 2020, but we will keep you updated as time passes. And not just about the release date—we’ll also be giving you sneak peeks and behind the scenes info on the book!”
It's a bit odd, though, that Goodman Games will be lurching from the Basic/Expert (B/X) Dungeons and Dragons line to the 1st edition Advanced Dungeons and Dragons line for S3, and then back to B/X for B4.