The proposed optimization is not solving the problem, it's just pushing the limits a little bit. I did a simple test similar to the reproducer and was able to generate a subclass proxy for a class with 2000 methods with the stable version of jboss-classfilewriter and 4000 methods with jboss-classfilewriter master (1.2) + https://github.com/jbossas/jboss-classfilewriter/pull/13.