Are they being fabbed by TSMC in the US, or overseas?

TSMC doesn't have any cutting-edge fabs in the US yet.

TSMC Washington is making 160nm silicon [0], and TSMC Arizona is still under construction.

[0] https://www.tsmcwashington.com/en/foundry/technology.html

That page doesn't really say much about what's currently being produced at TSMC Arizona vs the parts still under construction.

There's 4-nm "engineering wafer" production happening at TSMC Arizona already, and apparently the yields are decent:

https://finance.yahoo.com/news/tsmc-arizona-chip-plant-yield...

No idea when/what/how/etc that'll translate to actual production.

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Doing a bit more poking around the net, it looks like "first half 2025" is when actual production is pencilled in for TSMC Arizona. Hopefully that works out.

No disagreement here; the link I provided was specifically for TSMC Washington.

I'm not saying that TSMC is never going to build anything in the US, but rather that the current Lunar / Arrow Lake chips on the market are not being fabbed in the US because that capacity is simply not online yet.

2025H1 seems much more promising for TSMC Arizona compared to the mess that is Samsung's Taylor, TX plant (also nominally under construction).