24 years ago, then-CEO of Microsoft Steve Ballmer famously declared, “Linux is a cancer.” Ballmer’s bellicose rhetoric against Linux was part of a broader war by Microsoft on the very concept of open source software, especially the copyleft variety.

In history class, 24 years is not a long time. But in the tech world, it’s an eternity. And as it turns out, even the most pugnacious of hearts and minds in the tech world can change as drastically as the tech world itself over the course of a quarter century.

Today, Microsoft announced the launch of Azure Image Testing for Linux (AITL), a Linux distribution service for Azure developers. AITL is built on Linux Integration Services Automation (LISA), Microsoft’s open source tool designed to automate and enhance the testing and validation processes for Linux kernels and guest OS images on Azure.

This move is a significant milestone in what has been a monumental shift by Microsoft since Ballmer’s infamous comments in 2001. Microsoft’s evolving attitude towards open source isn’t simply a begrudging or reluctant acceptance that Linux isn’t going anywhere, it’s a full-on embrace that has elevated the Linux ecosystem itself. As of 2018, Linux–not Windows Server–is the most popular OS on Azure, which itself accounts for over 20% of the cloud infrastructure market.

Microsoft is perhaps the most prominent example of the broader industry trend of traditional proprietary software companies recognizing the commercial value of open source. Though we still haven’t reached the ‘hell freezing over’ moment of a full-featured, Microsoft-branded Linux distribution to compete with the likes of Red Hat or Ubuntu (though we may not be far off), Microsoft’s metamorphosis is still a surreal phenomenon to behold.