The California High Speed Rail Authority put out its 2026 business plan, which shows some pretty aggressive savings in the full line construction - $2 billion reduction for the initial Merced-Bakersfield segment, $10 billion reduction for the San Francisco-Gilroy segment, and huge cost reductions in Southern California by upgrading the existing Palmdale-Los Angeles commuter rail line instead of carving a new right of way.
While the Merced-Bakersfield savings are accrued through better project management, the big savings between San Francisco and Gilroy are done by reducing the maximum speed from 220 MPH to 110 MPH. The same goes for the Palmdale to Los Angeles section, eliminating a bunch of tunnels that were originally planned.
This is an intelligent move. At its core, a San Francisco-LA high speed rail line is really about building a 220 mph high-speed line between Gilroy, at the southern edge of the Bay Area, and Palmdale, at the northern edge of Los Angeles County. Something similar is happening with Brightline West, the privately funded bullet train from LA to Las Vegas. The fast part is from Rancho Cucamonga in San Bernardino County to Vegas, and it can reach LA proper via the existing San Bernardino commuter rail.
There are tradeoffs. Using the existing commuter rail tracks to approach LA and San Francisco makes the trip slower. An express train from the SF Caltrain Depot to LA Union Station is about 2 hours, 40 minutes with all the tunnelling originally planned. With the slower 110 mph sections, you lose about 20-30 minutes, making it roughly ~3 hours, 5 minutes from SF to LA by the express train.
The slower interim route shouldn't really discourage the High Speed Rail Authority from going forward with this plan. The biggest reason is simple: money. Even with the slower travel times, 3 hours from downtown to downtown is going to be a popular, lucrative route. (The 160 mph Acela Express which connects Boston, New York and Washington DC is highly profitable, despite running at slower speeds.)
I'm glad that the High Speed Rail Authority is thinking strategically about this stuff. Once the system is up and running and turning a profit, passengers will wonder how they ever lived without it.