It's super nice that they support moving up incrementally.

Moving to Swift-6 mode with full data-race safety checks can be daunting. They wrote a separate post on that, and Holly telegraphed that they're still actively reducing noise, i.e., warnings where the compiler could use a bit more analysis to prove there's no race.

The really nice thing is you can use the new tooling, but stay with the 5.10 version of the language that works for your code, and feature-by-feature add Swift 6 checking. You can build the same package under both language modes, so libraries can move ahead in their versioning while still supporting clients who are not ready.