What steps will reproduce the problem? As asm3.3.1 is widely used, I think latest kryo should keep compatiblity with it.

for once upated to asm4 many compatible problems forthcoming.

What is the expected output? What do you see instead? asm3.3.1 not support the latest kryo, maybe kryo could publish some compatible jars with it with the latest kryo.

What version of the Kryo are you using? kryo-2.20(but only 2.02 support asm3.3.1)

Please provide any additional information below.

If Kryo used ASM 3.3.1 then it would just cause compatibility problems for those using ASM 4.0. I think it is best to use the latest ASM. It all projects did this, there wouldn't be a compatibility issue. You can use Maven to create a "shaded" JAR, which has the ASM 4.0 classes renamed so they don't conflict with 3.3.1. Search the Kryo the mailing list or Google for making a shaded JAR.