Many older open-source programmers think, with reason, that's nonsense.
True, Apple has used open-source software for years, but that's not the same thing as making open-source development "a key part of its strategy." It would be more correct to say that Apple was the first major company to take advantage of open source.
Historically, Apple grows its software from open-source seeds, but the company's developers rarely contribute much code back.
The prime example of this is the Mac operating system. OS X is based on Darwin, a BSD Unix. Darwin started in 1996 with Steve Jobs' NeXTStep. Along the way to its official first release Cheetah in 2001, Mac OS X picked up a Mach 3.0-based microkernel that incorporated some of FreeBSD.
Instead of encouraging others to work on Darwin, which by itself isn't a working operating system, Apple dumped chunks of code weeks or months after each version of Mac OS X is released. For example, Apple released 10.11 "El Capitan", on September 30, 2015, but the latest OS X source code still isn't available.
This is not how open-source development works.
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The result is that the Apple-sponsored group that tried to turn Darwin into a working operating system, OpenDarwin, gave up trying in 2006. Its leaders wrote that the project had failed because of a lack of "availability of sources, interaction with Apple representatives, difficulty building and tracking sources" and the resulting lack of interest from its community.
What you get when you put it all together is that Apple is much more of an open-source user than a leader. So, who was the first "major" company to support open source? Well, you can argue it was Red Hat, founded in 1994; German Linux power SUSE, which got its start in 1996; or Corel, which in 1999 unsuccessfully released the first desktop Linux for the mainstream. But if you want to talk about really big companies supporting open-source I think the winner has to be IBM supporting Linux with a billion bucks in 2000. Even if you consider Mac OS X an open-source success, IBM beat Apple to the punch.
Apple, seeing which way the wind was blowing, made a rare public relations retreat. Instead of claiming to be the first open-source leader, it now reads: "'Open-source software is at the heart of Apple platforms and developer tools, and Apple continues to contribute and release significant quantities of open-source code."
That's still an exaggeration, but it's not the whopper that Apple had claimed earlier.