How long is the Commercial Activities long-stay visa valid, and what do I do after I arrive in Romania?

The Commercial Activities (business/investor) long-stay visa is issued for a 90-day window with one or more entries. It is the entry document, not your long-term status.

After you arrive, you apply to the General Inspectorate for Immigration for a residence permit, which is what actually lets you stay and run your business. This must be done before the visa expires, and applicants are expected to file shortly after arriving rather than waiting until the last days.

The residence permit is then renewed periodically, so the 90-day visa is best thought of as the first short step in a longer, renewable process.