The Java Class File API, currently a preview feature, marks a significant advancement in bytecode manipulation, offering a modern and streamlined approach for interacting with Java class files. This presentation provides an introduction to the Java Class File API, highlighting its key features and capabilities. We will compare it to ASM, the current de facto bytecode manipulation library, examining differences in design, usability, and performance. Additionally, we will analyze the potential impact of the Java Class File API on the Java ecosystem, including how it might influence the development of new tools, frameworks, and libraries, as well as its implications for existing ones that currently rely on ASM.