What 3D model formats are supported by ARKit?

The full set of file types documented as supported by the Model I/O framework can be found here:

https://developer.apple.com/documentation/modelio/mdlasset/1391813-canimportfileextension

The set of supported extensions and formats includes:

• .abc Alembic
• .usd, .usda, .usdc Universal Scene Description
• .usdz Universal Scene Description (Mobile)
• .ply Polygon
• .obj Wavefront Object
• .stl Standard Tessellation Language

Additional formats may be supported as well.

It looks like Apple's new preferred file type for ARKit on iOS (as of iOS 12) is their own usdz:

https://developer.apple.com/augmented-reality/quick-look/

DAE and OBJ/MTL are automatically supported, in the sense that you can just drop the files in the .scnassets folder and it will handle them for you. Personally, I had fewer issues with OBJ/MTL but I'm not well versed in 3D.

The documentation for Model I/O states that you can import 3D assets from the following files

The set of supported formats includes Alembic (.abc), Wavefront Object (.obj), Polygon (.ply), and Standard Tessellation Language (.stl). Additional formats may be supported as well.

I've not worked with this framework though, so can't tell you how well does it work with ARKit.

And you may want to have a look at AssimpKit which allows to export several formats to .scn SceneKit scenes

ARKit 5.0

ARKit itself doesn't read any 3D formats. Only rendering engines can do it.

SceneKit and RealityKit frameworks are satellites of ARKit, so they can read in poly geometry supporting several popular 3D file formats at the moment. If SceneKit or RealityKit can't read a file, you can covert it using usdzconvert Terminal command into USDZ.

• Collada's Digital Asset Exchange .dae (SceneKit)

• Pixar's Zipped Universal Scene Description .usdz (SceneKit and RealityKit)

• Pixar's ASCII Universal Scene Description .usda (needs conversion)

• Pixar's Binary Universal Scene Description .usd and .usdc (needs conversion)

• Reality Composer format .rcproject (RealityKit)

• Reality Composer format .reality (works faster in RealityKit)

• Wavefront Object .obj along with material .mtl (needs conversion)

• Alembic Interchange File Format .abc (needs conversion)

• Polygon File Format .ply (needs conversion)

• Autodesk Filmbox Format .fbx (needs conversion)

• Graphics Library Transmission Format .glTF (needs conversion)

• Stereolithography File Format .stl (needs conversion)

• Native Scene Format .scn (SceneKit)

The best way to use those formats is to initialize SCNScene from MDLAssset like this:

import SceneKit.ModelIO

guard let url = Bundle.main.url(forResource: file, withExtension: "usdz") 
else { 
    fatalError() 
}
let mdlAsset = MDLAsset(url: url)
let scene = SCNScene(mdlAsset: mdlAsset)