Updated: May 12, 2022.
SceneKit
Apple SceneKit framework handles 3D models for ARKit and VR apps. SceneKit supports the following 3D assets with corresponding material files:
.dae (with or without animations)
.obj (single-frame) with its texture and .mtl file
.abc (only single-frame supported)
.usdz (with or without animations)
.scn (native SceneKit's scene format)
RealityKit
Apple RealityKit framework also handles 3D models for ARKit, AR and VR apps. You can prototype a content for RealityKit in a standalone app called Reality Composer. RealityKit supports the following 3D assets:
.usdz (with or without animations)
.reality (with or without animations and dynamics) – optimized for a much faster loading
.rcproject (with or without animations and dynamics)
Additionally you can use Terminal's usdzconvert command to get .usdz from the following formats:
.obj
.glTF
.fbx
.abc
.usda
.usdc
.usd
And, of course, you can use Reality Converter app with its simple GUI.
Sceneform
Pity but since June 2020 Sceneform has been archived and no longer maintained by Google.
Google Sceneform handles 3D models for ARCore SDK. Sceneform supports the following 3D assets with their material dependencies:
.obj (with its .mtl dependency)
.glTF (animations not supported)
.fbx (with or without animations)
.sfa (ascii asset definition, deprecated in Sceneform 1.16)
.sfb (binary asset definition, deprecated in Sceneform 1.16)
SceneKit, RealityKit, Sceneform and Reality Composer support Physically Based Rendering.
ARKit and ARCore
But what's the role of ARKit and ARCore then?
These two AR modules don't care about importing and rendering of a 3D geometry. They are only responsible for tracking (world, image, face, geo, etc) and scene understanding (i.e. plane detection, hit-testing & raycasting, depth perception, light estimation, and geometry reconstruction).