> Worryingly, the two versions also produce different files That is actually pretty common. I would guess the version you have in macOS is an older version. Th

> Worryingly, the two versions also produce different files That is actually pretty common. I would guess the version you have in macOS is an older version. They may have tweaked the algorithm to deliver slightly better compression at the expense of speed, which is always the tradeoff in this field. On the other hand, I would not be surprised if they prepared special tweaks in their internal version to better support arm64. Strategically, Apple seems to believe that people will stick with building for their App Store if they are pushed to write non-cross-platform code. (Oddly enough, LZFSE/LZVN seems well-suited for file system compression on hard drives, but here again, Yann Collet wins with its LZ4's superior compression speeds, which impact write speeds.)