Nothing: healthcare.gov just believes what you tell it.
When you fill in your tax returns NEXT year (so 2026 for 2025) you 'fess up to what you actually got and then work out what “premium tax credit” you are allowed to claim.
For most people this means they get money back (just like the whole W4 fiasco).
If you can accurately predict your 2025 income healthcare.gov will accurately predict how much you need to pay for health insurance. For a T1D on a pump with a CGM it is even easier because you also know, accurately, what your health care costs will be. (healthcare.gov tries it’s best but most people don’t really know: we do.)
Basically most people get significant help with insurance premiums and some people get paid to take out health insurance. T1Ds with moderate income get some, quite significant, help but also get to pay for some, maybe all, of our additional costs pre-tax. That sounds complicated but compared to medicare, or traditional US health insurance, it is ridiculously simple.
Trust healthcare.gov. Answer the questions. We have 5 days.