Amazon Prime Instant Video has introduced Ultra HD content in the UK at no extra cost to the customer.
Blockbuster movies, hit TV shows and Amazon Original Series are now available to stream in the standard, which offers four times as many pixels as Full HD.
"We want to deliver the best entertainment experience, and offering Ultra HD movies and TV shows raises the bar on quality and innovation that customers have come to expect from Amazon," said Michael Paull, VP of Amazon Digital Video.
"We're also excited that Ultra HD is the latest benefit of the Amazon Prime membership, giving members instant access to great movies and TV shows in a premium picture resolution at no additional cost."
The move could tempt Netflix users to defect to the rival service, as they are charged a higher monthly fee for the privilege of accessing 4K video.
Free Ultra HD content on Prime Instant Video is limited at present, but includes Amazon Original Series Alpha House and Transparent.
A compatible television from LG, Sony or Samsung is required to view the content at the highest resolution.
