If you look at Redfin, the majority of the increase in inventory is downtown. Everyone who owns a smallish condo, is selling it, or attempting to right now.

Look at the places sold last month downtown, you'll see prices go under asking, or well below what they would have been at 6 months ago.

This is in stark contrast to the rest of San Francisco where inventory looks normal, but prices are 10-20% higher than they would have been 6 months ago.

What this tells me is this, people have more purchasing power because of lower interest rates and are selling their downtown condos to move out to the spacious parts of the city. (or moving further south)