Short answer: Cost-sharing reductions lower your deductibles, copays, and out-of-pocket maximum, but only on Silver marketplace plans and only for enrollees under a household-income threshold.
Cost-sharing reductions (CSRs) are a second ACA subsidy that lowers what you pay at the point of care, not the premium. They’re available only on Silver-level marketplace plans and only to enrollees with household income generally up to 250% of the federal poverty level who don’t have an affordable employer offer. Eligible members can receive both CSRs and premium tax credits at the same time.