Surprised to not see anyone talking about this on here so if I somehow missed a thread sorry in advance.
Yesterday Valve released Destinations Workshop Tools which can be downloaded on steam here. Now its made for vr headsets but you can quickly disable the forced vr mode using this guide. This is the closest we have to a source 2 sdk. I didn't mess with the dota 2 tools all that much so let me know if this is all old news. Definitely worth a look if your interested in the source 2 engine. No documentation on valve's dev wiki yet.
The sdk includes:
- New version of hammer
- material editor
- model editor
- particle editor
- source film maker
- steam workshop support
- vconsole 2
Some things worth noting:
I was able to import an old csgo map I was working on in the old hammer and it sort of worked! What others have been able to dig up about hl3, l4d, ect.