Python 3.15 ships lazy imports, sharper JIT

Python 3.15 is a pragmatic performance-and ergonomics release: lazy imports and interpreter improvements target real application startup costs, while the JIT remains an opt-in bonus rather than a reason to rewrite production systems.

• –Explicit lazy imports can reduce startup time, but libraries must test carefully for import-order and side-effect assumptions.
• –The upgraded JIT reports 7–8% gains on x86-64 Linux and 11–12% on AArch64 macOS in core benchmarks.
• –UTF-8 becoming the default removes platform-dependent behavior, but may expose applications that silently relied on legacy locale encodings.
• –The stable ABI for free-threaded builds is an important step toward distributing extensions across GIL-free Python versions.
• –Developers should test dependencies and compiled wheels before production upgrades; the release’s last-minute lazy-import fixes show why the extra release-candidate cycle mattered.