If it hasn't been tagged with a version yet, how do you know (or what makes you think) it's the same as this 'v1.4'?

I don't know for certain, but it seems likely that it is given that Jarred said "Claude Code v2.1.181 (released June 17th) and later use the Rust port of Bun".

What motive could he have for secretly maintaining a private fork of Bun that's shipped with Claude Code while simultaneously working on the open source repairs every day?