The last 13 gates of Phase 2 open tomorrow.
https://slcairport.com/assets/news/Media-Advisory_Phase-2-Completion.pdf
Per the press release, flight $394 to Atlanta will be the first to use the new gates.
I imagine this will shrink the hardstand operations significantly and also reduce the number of Delta flights in the B terminal. The last 3 Delta flights I've taken have been from the new gates opened earlier this year and it's been great.
Anyways, one more milestone and the last until the tunnel opens next October...