> Valve aren't really known for supporting their engines very well beyond their own internal needs.
Valve has a long history of supporting the modding community and outside users of Source, not sure where you're getting your information from but I don't think they've worked with the Source engine before. One of the biggest and most popular mods of all time was built on Source, and took the world by storm, with pretty big support by Valve through the years as well. Eventually they even bought the whole IP.
That was then, in 2025 they don't have a public Source 2 SDK, nor do they generally license the engine to third parties, S&box being the sole exception. They barely have their toes in the middleware game anymore.
Even when they were more open with their tech it was on the basis of "you can play with the tools we used to make Half Life and if your idea is sufficiently Half Life shaped then it will probably work", not trying to be a general purpose toolkit a la Unity.
S&B existing and being what it is, effectively makes it the Source 2 SDK, although it's not from Valve. But fair point Source 2 isn't licensed to others, I think the expectation is that if you wanna build a Source 2 game, you have to use S&B. At least for now, who knows what their ideas and ambitions really lie.
>They barely have their toes in the middleware game anymore.
Well they do have Steam Audio but yeah I agree. I think Epic is much better in this space, even though its only source available in practice they do a lot to support engine modifications and also accept external PRs. I think Valve has a lot to gain from open sourcing Source 2 and they should realize how important modding was to their initial success. The issue is now they can just print money with Steam so there is no need to invest in modding support.
There are various internal Valve tools that aren't available in any Valve-published SDK, but are in (accidentally?) within Dino D-Day's, a third party game based on Portal 2's version of Source.