[BjoernKW]

So, if I understand you correctly you'll be working on a contractual basis for a single client, full-time for a prolonged period of time.

This kind of arrangement indeed is quite likely to be classified as "bogus self-employment" by the German state pension system, no matter your legal setup. I wouldn't bother setting up a GmbH (private limited company) because it most likely won't help you anyway.

Unfortunately, there are no clear rules yet on when something is considered "bogus self-employment" and when it is not. However, there are some criteria for a setup to be more likely classified as "bogus self-employment" and other than the remote working part yours sounds more or less like the prototypical case.

The question remains, who would have to pay outstanding social security fees in that case. Usually it would be your employer. However, given that in your case they're in another jurisdiction social security might not be able to enforce that. Still, it might cause some trouble and costs for yourself (apart from the ethical issues that come with avoiding social security costs in such a manner).

The way remote employment (not consulting, which as you've mentioned, involves having multiple clients) could work relatively hassle-free in your case is your US employer setting up a company in Germany (a UG for example, which is a relatively cheap variation of the GmbH) and simply pay you from there, including taxes and social security like any other local employer.

[throwaway9283i]

I don't think that my employer would do so only for me (given that I don't even have an employer right now, I'm just speaking generally here). But I agree this would indeed be the best option.

Is there a way that I can pay the social security fees from day one on my own to completely avoid all hassle and possible back-payments after a Prüfung (audit)?

[leethargo]

As a hint: If you have been employed so far and are quitting your German job now, you have been paying into the "unemployment insurance". You can opt in to continue paying into that, voluntarily, but have to do so explicitly.

I didn't do that, regretted it later and wanted to return to it, but learned that the continuity is lost, that is, my income from the previous 12 months (when I was still employed in Germany) would not count for my unemployment payments.

[BjoernKW]

I suppose there are legal constructs that allow you to do this. For example, you could set up the UG mentioned above yourself and be its only employee with all the taxes and social security costs that implies.

However, that will get complicated rather quickly:

You’ll not only be that company’s sole employee you’ll also be its managing director. A managing director who owns a majority in the company usually is considered to be self-employed. A managing director also is responsible for filing annual accounts and tax statements. This is both expensive and time-consuming.

Another point to consider is that you’d effectively cover for employer’s share of the social security costs (unless they will be paying that on top of your salary, at which point they might just as well set up the UG themselves).

Not only is this a dodgy practice but you’ll also have pretty rough deal.

In any case, because this will get complicated you’d have to ask a lawyer who’s well-versed in both corporate law and social security law about the specifics.

It’d be much easier if they either were your client rather than your employer or if you were a co-founder.