If an EU citizen wishes to settle in Belgium, they must register with the relevant Belgian municipality. Since 1st September of this year, they have to submit all the necessary documents immediately. Previously, the persons had time to submit their documents for a maximum period of 3 months.
Source: vreemdelingenrecht.be, News, 21 August 2025
Available at: https://www.vreemdelingenrecht.be/nieuws/verblijfsaanvraag-unieburgers-alleen-mogelijk-na