Over the last few years, I have been working with the good folks at Apple’s Swift language team to adapt the ideas in my PLDI 22 paper “A Flexible Type System for Fearless Concurrency” to Swift. What started as a type system designed for dividing heap-allocated objects into a “tree of regions” has grown to a static-and-dynamic hybrid system intended to work in existing Swift code largely unmodified. In this talk, I will present a brief overview of the core technical content of the system (roughly as it appeared in the PLDI 22 paper), and then give an account of the changes we needed to interface correctly with Apple’s designers, developers, and devices. Throughout, I will attempt to characterize how my approach differs from (and is similar to) many ideas in the literature.