When generating class files in conjunction with `-target 9` (specified either explicitly or implicitly), `javac` will generate class files with a major version number of 53. For details of version 53 class files, see the _Java Virtual Machine Specification_.

The JDK classes themselves mostly use version 53 class files.

Tools or libraries that rely on ASM or other bytecode manipulation libraries may need updated versions of these libraries to work with version 53 class files.