In 2015, Microsoft acquired the Havok middleware software suite, which includes a physics component that's been used in hundreds of games going back over 20 years. This includes major releases from Valve including Team Fortress 2, Half-Life 2, and even Half-Life: Alyx. This has proved a barrier in that officially-supported Valve mods for these games then had to pay a hefty $50,000 license fee. In a good turn of news, it appears Valve has worked out a deal to remove these fees for modders going forward.
The news stems from the TF2CCWiki account on Twitter, which recently reached out to Valve asking for access for a license to its development repository. In response, Valve notified TF2CCWiki that it had recently completed an arrangement with Microsoft regarding the licensing of the Havok engine and its components. For Valve games specifically, licenses will drop the $50,000 fee and become completely free.
Valve went on to say that it sess the "purpose of mods" as noncommercial fan projects. Its message being that the $50k fee wasn't applicable to the vast majority of mods in the first place, since it'd only apply to premium, officially-sanctioned standalone mods. With that in mind, Valve said that its standards for the official support of a mod are extremely high. That's in part also due to the fact that the Team Fortress 2 development team doesn't have the "bandwidth" to manage mod teams individually. In other words, Valve is effectively saying, "Don't call us, we'll call you."
As such, while it's exciting news that Valve has been able to negotiate the removal of this licensing fee for the teams it works with, there are very likely few teams that had to pay it in the first place. Further, there will likely be very few modding teams that use it going forward.
What it should do is allow Valve to partner with more modding teams to officially sanction their work. That could mean more mods for Team Fortress 2, Half-Life: Alyx, and potentially other Valve game releases. However, whether Valve follows through with it and the results of those partnerships could be quite some time away.
How this arrangement came to be is certainly a particularly interesting subject, which of course there's no information on. Microsoft talking with Valve about mods and the Havok engine is a conversation few would expect to be ongoing. Yet that's exactly what's happened, leading to a better situation for Valve modders, at the very least.