Here's Sound Transit's current system:
https://www.soundtransit.org/get-to-know-us/maps
The largest agency is actually King County Metro, which operates most buses (including some semi-BRT, with more coming) and two streetcars. Current system:
https://kingcounty.gov/depts/transpo...ps/system.aspx
Sound Transit's expansion is outlined here. Current light rail expansions will go north and south (on the existing line) and east (co-locating on the existing line for a big segment). Future light rail expansions will to northwest (Ballard) and Southwest (West Seattle). They're also phasing in improvements to the existing north and south commuter lines, such as platform expansions to handle 10-car trains going south.
https://www.soundtransit.org/system-expansion
Tacoma has a streetcar they call light rail. It's built for short streetcars, not 380' Seattle trains. It's operating in an initial segment, and a second segment will open next year with a switchback up the big hill the core city is built on. (Personally I hope they keep the current express buses to Seattle, which travel at freeway speeds, currently beat commuter rail, and will beat light rail.)
Back on Seattle's Link Light Rail, two subway stations opened in October, but they're the last for a while. Current construction includes two tunnel segments on East Link, one using the existing I-90 tunnel and the other a new tunnel in Downtown Bellevue, but the stations are just outside the tunnels. The next phases (ST3) will include a third train tunnel through Downtown Seattle for the West Seattle to Ballard Link Expansion.
Confusing enough?