All B Gates will be completed in 24 months.

https://slcairport.com/assets/The-New-SLC-Images/The-New-SLC-Gate-count-at-a-glance-January-2024.pdf

Then once the airport hits 32M passengers in a year they'll build C gates. C gates won't open without a train that stops at A, B and C in the main tunnel. They've already built in the space for the train in the main tunnel. In 2023 SLC had 27M passengers. Sounds like they'll be close to 28M this year.

Likely means that by the the time B gates are done (2026), they'll start to re-locate the buildings where C gates would be and then start building C gates. They're going to want to get the C Gates and the train completely done by the olympics in 2034. My guess is that'll all be done by 2032 or sooner.

Why should you care?

Because it means more and better flight options from Delta (more European destinations, more Asia destinations, and likely more South American destinations). It also means more competition from other airlines which lowers prices.