PORTLAND — Amtrak’s Downeaster is celebrating its 10th birthday with $10 fares from Portland to Boston.

The fares, which are $5 less than the lowest published fare, are available on select runs next month. They’re available for purchase starting Thursday, the 10th anniversary of the first regularly scheduled run.

Also Thursday, Northern New England Passenger Rail Authority board members, transportation officials and other dignitaries will participate in an anniversary ceremony in Portland.

Existing stops between Portland and Boston are Old Orchard Beach, Saco and Wells in Maine; Dover, Durham and Exeter in New Hampshire; and Haverhill and Woburn in Massachusetts. Next year, the train will expand northward with additional stops in Freeport and Brunswick.