Fallout 4's impending next-gen update will almost certainly "break" many mods, according to a Fallout London modder, causing the "game-sized" project to be delayed indefinitely.

The Fallout London mod, which aims to depict the nuclear Wasteland in Englands capital, was due to release on April 23. Those plans have been shifted since publisher Bethesda recently announced that Fallout 4 would receive a beefy next-gen update just two days later, on April 25.

As project lead Dean Carter explains in the announcement video below, many Fallout 4 mods, including Fallout London, rely on the Fallout 4 script extender that will almost definitely break when the next-gen update launches. The Fallout London team will then need to wait for the team of modders behind the extender for fixes, meaning the release date is now up in the air.

"Everything has been set to go since our last update," Carter explains. "We've just been tweaking and testing non-stop in order to get things as stable as we can for you all in time for that release. But with the new update dropping just 48 hours later, the past four years of our work stand to simply break."

"Systems based on F4 SE, which for those unaware is the framework behind basically all of the dialogue systems in Fallout London and many of the other mods out there - that will break," Carter continues. Other new additions like the updated UI and new perks system will also "all require fixing after the update drops."

Carter says the modders at Team Folon are aware players can stop or bypass the update from installing, but the team "want this as close to a game release as we can."

The Fallout London project lead also offered a small update on the mod's release strategy. Fallout London is apparently around "30 to 40 gigabytes" in size, and so, it's simply "too big" to release on consoles or mod host website NexusMods. Fortunately, the team "now have a viable way to make the mod available for anyone who owns the game on GOG," but we'll need to wait a while more before anything is confirmed.