Only glanced through the paper on mutable value semantics (MVS). Which appears to be the differentiator of this from Rust.

The claim is that MVS enables mutable operations safely without the complexity of Rust - but still high performance.

"Mutable value semantics (MVS) sits at third point in the design space where both goals are satisfied and mutation is supported, without the complexity inherent to flow-sensitive type systems. The key to this balance is simple: MVS does not surface references as a first-class concept in the programming model. As such, they can neither be assigned to a variable nor stored in object fields, and all values form disjoint topological trees rooted in the program’s variables"