Which macOS version was the first free upgrade from Apple?

OS X Mavericks was Apple’s first major Mac operating-system upgrade offered free of charge. Released as OS X 10.9 on October 22, 2013, Mavericks was available through the Mac App Store to users running Snow Leopard 10.6.8 or later.

The change ended Apple’s long-running pattern of charging for major OS X upgrades. Earlier releases, including Lion and Mountain Lion, were inexpensive compared with traditional boxed software, but they still had purchase prices. Mavericks made the upgrade free for compatible Macs, and Apple continued the policy with later releases such as OS X Yosemite and OS X El Capitan.

Mavericks also began Apple’s California-location naming era, replacing cat names such as Leopard and Mountain Lion. It was named after the famous surfing location in Northern California and introduced features including Finder Tabs, Tags, iBooks, Maps, and improved power management. El Capitan and Sierra were also free, but they followed Mavericks rather than establishing the policy.