That's sort of what is happening. Government is guaranteeing $1.6B of Constellation's loans.

Constellation is sourcing a loan themselves, but if they can't pay, government will pay $1.6B of what is left owing.

This makes Constellation's loans cheaper

Aside from that, existing policy of government paying part of the cost of clean* power means Microsoft will pay less for the power

So taxpayers are on the hook for one and a half gigabucks if Constellation goes bust

Taxpayers are also on the hook for part of the cost of the power produced