When and how exactly will Tokamaks be able to contain plasma for more than a few minutes?

As I understand it, no controlled nuclear fusion reactor has ever succeeded in containing plasma for more than a few minutes at a time. The two main problems that have existed since controlled nuclear fusion research commenced nearly a century ago, have been producing more energy than consumed, and producing energy steadily over a prolonged period of time, as any commercially viable power source would certainly have to do. The ITER controlled nuclear fusion project in France is supposed to largely solve this first problem -- in theory, this Tokamak should be capable of producing ten times the energy it consumes, at the cost of tens of billions of dollars, assuming it is ever actually completed, and assuming that it works exactly as it's supposed to work. However, as I understand it, even the ITER project is not supposed to be able to operate for more than 400 seconds at a time. In other words, it will still, quite certainly, be very, very far from a practical design for an actual nuclear fusion power plant. Now, I realize of course that these are all experimental designs that are only supposed to produce energy in spurts. Fair enough. However, does anyone actually have any idea how to build a nuclear fusion power plant that would actually constitute a practical design for a commercially viable power source, that would be marketable in practice? And, I don't mean simple claims for this. Anyone can claim their design does anything they like, that doesn't mean it's actually true, at all. Is there any clear evidence of a path to an actual, commercially viable nuclear fusion power source using Tokamaks, that can work steadily for years at a time, and not just seconds?