Does a US LLC operating agreement have to be in writing?

It depends on the state of formation. Under 6 Del. C. § 18-101(9), a Delaware limited liability company agreement may be written, oral or implied, and binds members, managers and the company whether or not they execute it. New York Limited Liability Company Law § 417(a) instead provides that members shall adopt a written operating agreement, and § 417(c) allows it to be entered into within ninety days after the articles of organization are filed.

Can fiduciary duties be waived in a US LLC agreement?

In Delaware and Texas, yes; in California, no. 6 Del. C. § 18-1101(c) allows duties including fiduciary duties to be expanded, restricted or eliminated, but not the implied contractual covenant of good faith and fair dealing. Texas Business Organizations Code § 101.401 permits the company agreement to expand, restrict or eliminate any duties including fiduciary duties. California Corporations Code § 17701.10(c)(4) prohibits eliminating the duty of loyalty, the duty of care or any other fiduciary duty.

Must a US LLC report its beneficial owners to FinCEN?

Not if it was formed in the United States. FinCEN's interim final rule published in March 2025 exempts all entities created in the United States, including those previously described as domestic reporting companies, and their beneficial owners, from the requirement to report beneficial ownership information. The definition of reporting company was narrowed to entities formed under the law of a foreign country that register to do business in a US state or tribal jurisdiction.

LLC Operating Agreement in the US

The most consequential drafting decision for a United States LLC is which state's act governs, because the states disagree about whether fiduciary duties can be waived. Delaware and Texas both allow an agreement to eliminate fiduciary duties entirely, subject in Delaware to the implied covenant of good faith and fair dealing. California's Revised Uniform Limited Liability Company Act prohibits it outright. New York goes in the opposite direction and requires members to adopt a written operating agreement at all.

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Governing law

The LLC statute of the state of formation governs the agreement and the internal affairs of the company. There is no federal LLC law.

Delaware Limited Liability Company Act, 6 Del. C. § 18-1101

What a llc operating agreement has to contain in the US

In Delaware a limited liability company agreement may be written, oral or implied, a member or manager is bound whether or not they execute it, and the company itself is bound whether or not it executes it.
6 Del. C. § 18-101(9)
Delaware policy is to give maximum effect to freedom of contract, and duties including fiduciary duties may be expanded, restricted or eliminated, except that the implied contractual covenant of good faith and fair dealing may not be eliminated.
6 Del. C. § 18-1101(b) and (c)
A Texas company agreement may expand, restrict or eliminate any duties, including fiduciary duties, and related liabilities owed by a member, manager, officer or other person to the company or to a member or manager.
Tex. Bus. Orgs. Code § 101.401, as amended by S.B. 29 (2025)
A California operating agreement may not eliminate the duty of loyalty, the duty of care or any other fiduciary duty, and may not eliminate the contractual obligation of good faith and fair dealing, though it may prescribe standards for measuring performance if they are not manifestly unreasonable.
Cal. Corp. Code § 17701.10(c)(4) and (c)(5)
In New York the members of a limited liability company shall adopt a written operating agreement covering the business of the company, the conduct of its affairs, and the rights, powers, preferences, limitations and responsibilities of its members, managers, employees or agents.
N.Y. Limited Liability Company Law § 417(a)

Form, notarisation and registration

A New York operating agreement may be entered into before, at the time of, or within ninety days after the filing of the articles of organization, and may not become effective before the company is formed.
N.Y. Limited Liability Company Law § 417(c)

What catches drafters out

Beneficial ownership reporting no longer applies to US-formed LLCs: FinCEN's March 2025 interim final rule exempts all entities created in the United States and their beneficial owners, narrowing the definition of reporting company to entities formed under foreign law that register to do business in a US state or tribal jurisdiction.
FinCEN, Removal of beneficial ownership reporting requirements for US companies and US persons
A California operating agreement also cannot vary the law applicable to the company or the power of a court to decree dissolution in the circumstances specified in the act, so choice of law clauses face limits Delaware does not impose.
Cal. Corp. Code § 17701.10(c)(2) and (c)(7)