ECs start life as public housing
Executive Condominiums are developed by private developers but sold under HDB eligibility rules and subsidy schemes, similar to BTO flats. This means income ceilings, eligibility schemes and MOP all apply, just as they would to an HDB flat.
MOP for ECs
ECs carry the standard 5-year MOP, during which you cannot sell, rent out the whole unit, or buy other property, the same as any HDB flat.
Privatisation timeline
After a further period from the completion date (generally around 10 years from TOP in total), an EC fully privatises — at which point it can be sold to foreigners and PRs without the restrictions that apply to HDB flats and pre-privatisation ECs, and HDB-specific resale rules (like the resale levy) no longer apply to that later sale.
If you're comparing a resale HDB flat against a new EC launch, remember the EC won't be sellable at all until MOP completes, and won't be open to the full private-property buyer pool until full privatisation — factor both dates into your exit planning.