Looks like they figured it out after one of the compiler guys looked at the code https://discord.com/channels/280713822073913354/104933911236... ------ So I took a look at the code and the generate bytecode to try to see if the Scala 3 compiler was generating significantly more code. I don't see anything too weird, but the one thing that stands out is all the inline given Conversion in the codebase. I assume the idea is to use inline for performance but I'm afraid it's counter productive here: you end up inlining the anonymous class creation, so every usage of a conversion ends up creating a new anonymous class. So I recommend just dropping the inline keyword when defining a given ... =