PHP 8.0 introduced a JIT (Just-In-Time) compiler as part of OPcache, translating hot bytecode paths into native machine code at runtime for CPU-bound workloads. It's configured via opcache.jit and opcache.jit_buffer_size in php.ini.
JIT provides the biggest wins for CPU-intensive numeric/computational code; typical I/O-bound web applications (dominated by database and network calls) see comparatively modest improvements from JIT alone.