$11.58 million is the lifetime exclusion from owing estate tax on the value of the decedent's estate.
See https://www.irs.gov/businesses/small-businesses-self-employed/estate-tax
A revocable (aka living trust) becomes irrevocable at the death of the grantor and a separate taxable entity. As such, the the trust is required to file Form 1041 if the trust has any taxable income for the tax year or gross income of $600 or more.
See https://www.irs.gov/instructions/i1041#idm140229124997744
