A lot of this has changed with the No Surprises Act, that specifically covers Emergency situations and others where a patient would be "reasonably expected" to believe that a service was in network.
Surprise billing protections apply to most emergency services, including those provided in hospital emergency rooms, freestanding emergency departments, and urgent care centers that are licensed to provide emergency care. The federal law also applies to air ambulance transportation (emergency and non-emergency), but not ground ambulance.
It also covers non-emergency services provided by out-of-network providers at in-network hospitals and other facilities. Often, the doctors who work in hospitals don’t work for the hospital; instead they bill independently and do not necessarily participate in the same health plan networks.
Doesn't mean your insurer might not deny coverage or apply a deductible that you have to fight.
You also cannot waive certain rights. Like some hospitals will try to get you to sign waivers around balance billing, and in/out network discrepancies. Some of these will vary by state, so be aware.
> The No Surprises Act (NSA) establishes new federal protections against surprise medical bills that take effect in 2022. Surprise medical bills arise when insured consumers inadvertently receive care from out-of-network hospitals, doctors, or other providers they did not choose. Peterson-KFF and other studies find this happens in about 1 in 5 emergency room visits. In addition between 9% and 16% of in-network hospitalizations for non-emergency care include surprise bills from out-of-network providers (such as anesthesiologists) whom the patient did not choose. Surprise medical bills pose financial burdens on consumers when health plans deny out-of-network claims or apply higher out-of-network cost sharing; consumers also face “balance billing” from out-of-network providers that have not contracted to accept discounted payment rates from the health plan.
Source: https://www.kff.org/health-reform/issue-brief/no-surprises-a...