Dfyjkt

I am planning to visit Saint Petersburg alone for 4 or 5 nights and stay at an AirBNB. Now, I am obtaining my invitation via a travel agency. I am not sure if they can register me once I arrive in Russia, but my hosts have declined to register me upon arrival. Some also claim that since I am going to stay for less than 7 days, I can choose not to register myself.

But just to be safe, how does one register himself if the hosts or the agency are not going to be of any help? In such a case, how do I exit the country or deal with police if stopped, if I do not register myself with the Federal Migration Services?

UPDATE:

Just got back. I did not have to register since I stayed for 3 business days and 2 holidays (Saturday and Sunday). I was not asked anything on exit but handing the Migration Card which was given upon entering the Russian Federation. Hope this helps future travelers.

Here it is stated that your responsibility is to register after 7 workdays of staying at your temporary accommodation (paragraph 2., item 2)):

1. Иностранный гражданин в случае нахождения в месте пребывания обязан встать на учет по месту пребывания в порядке и на условиях, которые установлены в соответствии с настоящим Федеральным законом или международным договором Российской Федерации.




2. Постановке на учет по месту пребывания подлежат:

2) временно проживающий или временно пребывающий в Российской Федерации иностранный гражданин - по истечении семи рабочих дней со дня прибытия в место пребывания, за исключением случаев, когда указанный иностранный гражданин:

(Additionally they display an icon that leads to clarifications on the paid version of the site, have no idea of what that could be.)

The text further says that you have to immediately (on the day one) notify FMS of your arrival in case you don't have any specified accommodation, but I suppose you have at least the confirmation from your hosts sent via AirBnB, so that should qualify.

In such a case, how do I exit the country or deal with police if stopped, if I do not register myself with the Federal Migration Services?

You'll probably have your migration card at hand which you should fill at arrival, that would be a paper confirmation of the longevity of your stay.

Foreigners visiting Russia for less than 7 days are not obliged to register (unless they stay in a hotel of some medical institution. But 1) it's not your case since you are going to stay at someone's place, and 2) hotels are obliged to register foreigners themselves).

Глава 4. УЧЕТ ИНОСТРАННЫХ ГРАЖДАН ПО МЕСТУ ПРЕБЫВАНИЯ

Статья 20.

6. Не подлежат учету по месту пребывания:

5) иные иностранные граждане, прибывшие в Российскую Федерацию на срок не более семи
дней, за исключением случаев нахождения указанных иностранных
граждан в гостинице или в иной организации, оказывающей гостиничные
услуги, в санатории, доме отдыха, пансионате, кемпинге, на туристской
базе, в детском оздоровительном лагере, медицинской организации,
оказывающей медицинскую помощь в стационарных условиях, или
организации социального обслуживания.

Full text (Russian).