No, retirement plans are trusts and although somewhat different from the typical irrevocable trust are taxable entities and mist file using IRS form 5500.
DOL (Dept of Labor), IRS and PPBGC (Pension Benefit Guaranty Corp.) jointly developed the Form 5500 Series so employee benefit plans could utilize the Form 5500 Series forms to satisfy annual reporting requirements under Title I and Title IV of ERISA
and under the Internal Revenue Code
In terms of the more typical trusts that are used by individuals and Corporations to segregate assets, for estate planning
, charitable needs and special needs planning, it comes down to one thing; ... whether the grantor of the trust has any discretion to direct or use trust proceeds. Truly irrevocable trusts such as these use form 1041 and pay taxes based on the tax brackets for trusts (IRS publishes tax brackets and rates for (1) individuals, (2) corporations and (3) trusts).
Revocable trusts, very much like S-Corps, LLC;s and partnerships are pass-throughs, and are taxes are passed through to the owner/grantor's personal tax
Qualified plan reporting:
Trust - and estates - reporting (irrevocable):
Where all income for revocable trusts, LLC's, Sole Proprietorships, partnerships and S-corps end up; the 1040 (or one of it's versions)
We should not forget that Federal estate and gift taxes
are paid using
form 706 (estates) and form 709 (post 1976 taxable gifts
I provide this as an overview. Each of these forms have exceptions, caveats and multiple possible supporting documents and scheduls.
But hopefully this gives a feel for how it all works.
Circling back to your original question, essentially trusts are either taxed as their own entities or to the grantor, depending on whether the grantor has truly given up all present interest.