Python's import tax measured across 63,431 runs, and 3.15's lazy mode breaks 8 of 414 top packages.

The first systematic measurement of PyPI import cost covers the 500 most-downloaded packages sampled quarterly over five years, under CPython 3.9 through 3.14, on Apple M5/macOS and Intel Xeon/Linux. Half of packages import in under 6 ms but p99 is 354 ms. First import after installation costs 3-22x more because of bytecode compilation. Importing a package's submodules can cost up to 294x the top-level import that benchmarks report. Median cost grows 1.6-2.4%/year while mean grows 11-13%/year. A single point release (3.11.5 against 3.11.16) swings cost by 1.34x. PEP 810 global lazy mode in 3.15 makes imports essentially free and breaks 8 of 414 top packages.