[DennisP]

Do you believe MIT? They used to run the Alcator C-Mod, which had the highest magnetic field of any tokamak in the world, did preliminary work with the new superconductors, and based on all that they designed ARC before they spun off a company to actually build it.

[phtrivier]

I'll believe whoever first powers a light bulb from fusion.

I can completely imagine that it goes through stages like

Half a century of painful research at universities -> decades to build multiple prototypes -> years to build a POC -> decades to industrialize the POC -> years to connect the POC to the grid -> ???? -> light bulb moment -> ???? -> profit

I'm not sure we much further than the beginning of step 2. Indeed, (sorry to say that), I'd trust an MIT startup to do that more than a YC startup. But real life will serve as evidence.