After seeing its announcement a few days ago I didn’t think much of it, but after looking into it a bit this looks awesome !
Box3D was released a few days ago by legendary developer Erin Catto accompanied by a blog post, this is the person behind the popular Box2D engine.
In the blog post he explains that his work stems from his collaboration with Dirk Gregorius, “Principal Software Engineer II and Physics Architect” at Valve, the person behind Half-Life: Alyx’s physics engine “Rubikon”, which Box3D is based off.
Facepunch has also revealed that they have been using Box3D for about a year now as well in s&box. Showcasing a cool demo
An interesting quote from the blog post:
On the Valve side, Rubikon continues to evolve and Dirk has developed optimizations (similar to those in Box3D) in a new engine called Ragnarok. Look for that in future Valve games.
👀
Did he just reveal Valve’s next physics engine ?
+HL3 confirmed
- cool showcase 1
- showcase 2
- showcase 3 in gmod (already??)
Tweet transcript
I’m happy to announce the release of a new open source 3D physics engine called Box3D. I’ve been working on this project for a few years now, but it represents over 20 years of experience writing physics engines for games. Read more here: [blog post link]



Alyx’s physics were genuinely groundbreaking. If this includes all the features they showed off in that game, it’ll be one hell of a contender in the physics engine market.
Though it would have been more impactful (ha) if they had released it six years ago alongside Alyx, back when the free physics options were all kind of crap compared to the commercial ones. Jolt has become the de facto free 3d physics solution within the past few years and it’s also a huge step up over the old offerings.
Edit: sadly it seems Box3D is based on a stripped-down version of Rubikon and doesn’t really do much beyond extend Box2D to the third dimension. I guess its selling point is that it’s probably much, much easier to integrate than Jolt, and that the API will be familiar to Box2D users.