The Mill grant-based model is semantically quite similar to capabilities, but it associates protection with the accessor (thread/turf) rather than the access (pointer/capability). This lets us preserve the size of a pointer, which no one knows how to do efficiently with capabilities.

The difference between the two models is visible when you pass a graph structure across a protection boundary. With caps is is easy to pass the whole graph, and hard to pass only one node. With grants it is vice versa.