[dragonwriter]

> locks will still be needed within multithreaded guilds

It seems to me that is the intent; that is, any Ruby code that exists now is single-guild Ruby 3 code -- if its multithreaded, it needs locks, for the same reason it does now.

> It would seem like the intention would be to replace usages of Thread with Guild to avoid the concurrency issues inherent with threaded code

I think that'll be a common use case, though running what amount to multiple "legacy" Ruby 2 multithreaded systems in separate Guilds in the same Ruby 3 process seems also to be an intended supported use case.

> Will there be API support to create a Guild that only allows a single thread?

It certainly sounds like a good idea.