Registration at Commune - Is apartment lease necessary?

Yes. Housing contract is required. There are many threads in the forum (https://www.expat.com/forum/viewforum.php?id=256) discussing the whole registration and RP process.

Housing contract is npt required, proof of housing is.

Register where you are currently living, bring proof of where living.

Hi folks,
I found this old thread is talking about my problem, but it was in the old work permit, all posts Aneesh put were talking earlier than 2019, so what about single permit process? My passport was stamped a new stamp that I have to register my self in the commune within 8 days from arrival and I booked 1 month using Airbnb which isn't official address like house rental or hotel, so if I stayed until I got an official address, I guess the commune will see the stamp of entering the country and may ask why did you get late in registering, what should I say? Also if I went to the commune as soon as I arrive, can I just give them the address with Airbnb receipt and tell them that this what I have for now? What will happen then?

Any help will be highly appreciated!

Current laws regarding airbnb in Belgium are completely outdated. New laws should come soon when we'll have a government...
I think it shouldn't be a huge problem if you stay temporary there and if it is not assimilated as a "long term rent" of an apartment/house.

Keep in mind, that hotels MUST inform immigration/local police if a foreigner is in their hotel. (like in any country)
I'm not sure it's the case for airbnb as it is a temporary rent from person to person.

So, go to your commune with your booking (+ proof of payment) and state that this is a temporary address.
They'll notice you that you must come back after the "lease" period is over, to state again the current and/or new address. You've to tell them immediately when you change your address.
They might also tell you to inform the local police of your presence at the address, as it's an airbnb rent. (Commune and local police should communicate together, so it will probably won't be needed)

In the end, they just want to know exactly where you are temporary living until you get an apartment/house...