tl;dr – This is an update to the Bahraini carrier’s previously announced initial order.
Gulf Air and Boeing recently announced an update to their previous purchase agreement with the Bahraini carrier, confirming an order of fifteen 787s, with the option to purchase an additional three.

Gulf Air recently started flying to New York’s JFK in October, with three times weekly service. It’ll be interesting to see how these additional aircraft factor into the airline’s global expansion strategy, including the possibility of resuming previously terminated long-haul routes.