Python 3.15’s Ultra-Low Overhead Interpreter Profiling Mode

CPython 3.15's JIT uses a clever new technique called dual dispatch to profile the interpreter with minimal overhead. Instead of running two separate interpreters or using slow conditional branches, it swaps dispatch tables at runtime, routing all profiling through a single instruction. This keeps profiling overhead to just 4.5x slower, compared to 900x–1000x in systems like PyPy.