They should automatically get applied on the healthcare.gov site or your states local version. They only apply to the silver level plans, which is why the GGP post talking only about bronze and gold plans quoted such high numbers. Those plans completely skip the subsidies.
That's why the websites ask you your income levels.
It also affects your max out of pocket expenses for the year (total limit of deductibles and copays before insurance has to cover it all)
They are computed from a given state's 2nd-most expensive silver plan, but they apply to all plans. I am on a gold plan and receive them; last year I was on bronze and received them.
The subsidies have no impact on deductibles or OOP - that is determined by the insurance plan itself.
I looked it up, and we are both correct. There is a premium subsidy based on the silver plan but that applies to any plan and a deductibles/OOP pocket subsidy that only applies to the silver plan. They have different qualification levels. It seems the deductibles level has a pretty low income cutoff, and the premium subsidy has changed a lot over COVID (to the point where the income limit was removed, at least temporarily).
That's why the websites ask you your income levels.
It also affects your max out of pocket expenses for the year (total limit of deductibles and copays before insurance has to cover it all)