Tagged pointers don't buy as much performance as you'd expect in Java. That's because the JVM is highly multithreaded, and the Java memory model guarantees memo

Tagged pointers don't buy as much performance as you'd expect in Java. That's because the JVM is highly multithreaded, and the Java memory model guarantees memory safety (unlike in Go, for example). So every pointer load from RAM will need a check for the tag bits. And you end up with your code full of branches. From practical experience, JVMs have had an option to use compressed pointers for inner fields for two decades ( https://wiki.openjdk.org/display/HotSpot/CompressedOops https://wiki.openjdk.org/display/HotSpot/CompressedOops ). It saves a bit of RAM, but often results in slower code. More recently, the new ZGC collector started using colored pointers, there's a good presentation about it: https://inside.java/2025/10/06/jvmls-zgc-colored-pointers/ https://inside.java/2025/10/06/jvmls-zgc-colored-pointers/ It's also been a mixed bag, performance-wise.