Workplace pension reporting to IRS

I'm moving to the USA for a bit (so will be a US tax resident) and have a UK DC workplace pension, and I'm a little bit confused on what the reporting requirements are with the IRS. For clarity, by DC workplace pension I mean those in which an employer auto-enrolls you and to which the employer contributes some and you can contribute via salary sacrifice. I then invest the contributions in funds with the provider (in my case L&G).

Most issues I've seen seem to speak about SIPPs, leaving me a bit in the dark on vanilla workplace pensions. Some advice seems to suggest that moving to a SIPP would trigger additional filing requirements, which implies that leaving it alone would not, but I'd like to get some clarity/advice on what people are doing.

Obviously I need to file FBAR and 8938 (provided the amount is high enough).
I probably should file 8833 to claim deferral of gains under article 18 of the tax treaty, just to be safe.
But what about 3520 and substitute 3520A? I know there is a lot of discussion on whether this applies to SIPPs or not, and whether Revenue Procedure 2020-17 provides any relief. However, I've seen little discussion on whether a workplace pension would trigger these filing requirements. I don't even know if I'll be able to find enough information to complete a substitute 3520A.

Is a workplace pension structured as a trust in the UK? Would the IRS consider it a trust?

Fortunately, as I'll be living in the USA, I won't need to think about making contributions, and fortunately I'm long enough away from retirement that I don't need to think about distributions.

FWIW, my son has a workplace pension plan in which he matches but doesn’t exceed his employer’s contributions. Other than FBAR he doesn’t do anything else. (Threshold is below 8938 reporting). He doesn’t file form 8933 to claim a treaty exemption and I’m near certain that form is not needed, nor does he file form 3520, the Foreign Grantor Trust form.

It's been some time since I looked at this, and you'll want to check to see if I'm correct or if anything has changed, but when I was investigating for my daughter about the status of her very small uk private sector pension account, because the employer had put in half or more than half of the funds in the account, she did not have to do any reporting on it to the IRS. Once she takes the money out, assuming it still exists several decades from now, she would be taxed on it as income.

I've contributed about 65% of the value, so looks like I'm in for 3520/3520A :/

I've contributed about 65% of the value, so looks like I'm in for 3520/3520A :/

Not necessarily, it is complicated.

https://www.thetaxadviser.com/issues/2020/may/foreign-pension-plans-us-uk-tax-treaty.html

Employees' trust: If a pension plan is more than 50% funded by the employer and the plan does not favor highly compensated employees, the foreign pension is considered a nonexempt employees' trust and governed by Sec. 402(b). In that case, employer contributions are generally taxable income to the employee, but growth inside those plans is tax-deferred until distribution. Upon distribution, the fund functions like an annuity under Sec. 72, and the taxpayer would be allowed to recover his or her basis (contributions) as a return of capital. However, if one of the reasons a trust is nonexempt from income tax is a failure of the plan to meet the participation requirements of Sec. 401(a)(26) or the coverage requirements of Sec. 410(b), then a highly compensated employee shall, in lieu of the contribution amount to the plan under Sec. 402(b)(1) and distributions from the plan under Sec. 402(b)(2), include in gross income an amount equal to the vested accrued benefit as of the close of the tax year of the trust. Thus, the highly compensated taxpayer will end up including in gross income the incremental increase in the value of the plan as of the end of each year. The meaning of "highly compensated" for these purposes is set forth in Sec. 414(q). This amount is adjusted for inflation each year and for 2020 equals $130,000.