Sony developed the 4K Digital Cinema format and provides a list of the movies filmed in 4K on its product website, us.digitalcinema.sony.com. The titles listed date back to 2011.
Other lists are available, but are not as authoritative as the Sony list. Amazon.com's list of 4K movies does not distinguish between movies filmed in 4K and those mastered in 4K. Wikipedia's list does not distinguish between movies filmed in other digital formats. User-generated lists on IMDb.com are outdated and may not include all 4K movie titles.
No list other than Sony's own list includes titles that have not yet been released in theaters.