OpenAPIKit v6 introduces no breaking code changes.
The minimum Swift version has increased to Swift 6.1.
The external loading capabilities introduced in OpenAPIKit v4.0.0 have been moved into a Trait. The trait is enabled by default, but you can disable it if you don't want to use the external loading features and you want to save some time compiling OpenAPIKit. The Swift compiler is notably slow to compile Swift Concurrency features so turning the trait off can save around 50% of the compile time.
There is no known runtime cost to the trait being on, just the compile time cost.