March 30, 2020 Facepunch Studios has confirmed the game being referenced is Sandbox.
It looks like Garry's Mod 2 is in the works - sort of. The creator of the original Garry's Mod - or GMod, for short - has teased that he's "making GMod 2" on Twitter via a meme (that familiar Distracted Boyfriend one), but it seems the game he's referencing is Sandbox.
Garry Newman's post on Twitter seems to tease he's "making GMod 2", as you can see below, though it's not exactly confirmed at this stage. In a follow-up tweet the dev, who is based at Rust studio Facepunch in the UK, jokes: "Holy s***, thanks for the support, hope you're not gonna be disappointed when you find out that GMod2 is an iOS match 3 game made in unity." It's not clear what form GMod 2 might take just yet, but we're pretty sure it's not that.
However, we reached out to Facepunch and it seems the game being referenced in the tweets is actually Sandbox (or S&box), a new Unreal Engine tool the studio has been working on for several years. "Our intention with Sandbox is to take a powerful game engine (UE4 right now) and build a hotloading C# layer on top of it," the site's description of Sandbox reads.