If I'm not mistaken the Reactor implementation relies on an unbounded buffer under the hood, but that is not the case for KotlinX Flow. The buffered callbackFlow has a buffer size of 64 by default.

You could set an explicit buffer size of UNBOUNDED but the user can overwrite with the buffer operator, so that would have to be avoided by preventing that or it should use trySendBlocking instead.

I think back pressuring the LLM messages makes no sense, so an unbounded buffer size is probably desired. If desired I can provide a PR with a fix.