So, how can you watch? Well, you'll need a compatible TV (or other device) and a suitably high-speed internet connection. And you'll also need to be a rapid responder, as it won't be available to everyone. Read on for all the details.
4K iPlayer: what can you watch?
All 29 of BBC One’s World Cup matches will be available in 4K Ultra HD and High Dynamic Range (HDR). The BBC is showing 33 World Cup matches in total across BBC One, Two and Four, with the distinction here being those that are shown on BBC One. It's these games that will be available on iPlayer in 4K.
There's no word as yet on whether any other 4K content will be available after the World Cup. Previously the BBC has delivered 4K iPlayer trials of live Rugby League and FA Cup football, and looking ahead on the BBC Sport schedule, the Wimbledon tennis tournament could present a further 4K opportunity.
The World Cup trial will be "first come, first served". The Ultra HD stream will be available from the BBC iPlayer home screen when coverage begins and until the trial is full for that match. The BBC has said the trial will be available to "tens of thousands of people".
We know that the recent 4K iPlayer trials have been centred around "stress-testing" the service - checking how many people it can handle streaming 4K video at the same time.
The 2018 FIFA World Cup kicks off on Thursday June 14th at 4pm BST (ITV will show the opening match plus the opening ceremony), but these following 29 BBC One matches are the ones that will be available in 4K on iPlayer.
Friday 15th June Egypt v Uruguay (A) 1pm (BBC One)
Friday 15th June Portugal v Spain (B) 7pm (BBC One)
Saturday 16th June France v Australia (C) 11am (BBC One)
Saturday 16th June Peru v Denmark (C) 5pm (BBC One)
Sunday 17th June Germany v Mexico (F) 4pm (BBC One)
Monday 18th June Belgium v Panama (G) 4pm (BBC One)
Monday 18th June Tunisia v England (G) 7pm (BBC One)
Tuesday 19th June Colombia v Japan (H) 4pm (BBC One)
Tuesday 19th June Russia v Egypt (A) 7pm (BBC One)
Wednesday 20th June Portugal v Morocco (B) 1pm (BBC One)
Wednesday 20th June Uruguay v Saudi Arabia (A) 4pm (BBC One)
Thursday 21th June Argentina v Croatia (D) 7pm (BBC One)
Friday 22nd June Nigeria v Iceland (D) 4pm (BBC One)
Friday 22nd June Serbia v Switzerland (E) 7pm (BBC One)
Saturday 23rd June Belgium v Tunisia (G) 1pm (BBC One)
Sunday 24th June England v Panama (G) 1pm (BBC One)
Sunday 24th June Japan v Senegal (H) 4pm (BBC One)
Monday 25th June Spain v Morocco (B) 7pm (BBC One)
Tuesday 26th June Nigeria v Argentina (D) 7pm (BBC One)
Wednesday 27th June South Korea v Germany (F) 3pm (BBC One)
Thursday 28th June Senegal v Colombia (H) 3pm (BBC One)
Sunday 1st July 1B v 2A (Match 51) 3pm (BBC One)
Monday 2nd July 1E v 2F (Match 53) 3pm (BBC One)
Monday 2nd July 1G v 2H (Match 54) 7pm (BBC One)
Tuesday 3rd July 1H v 2G (Match 56) 7pm (BBC One)
Friday 6th July Winner 49 v winner 50 (57) 3pm (BBC One)
Friday 6th July Winner 53 v winner 54 (58) 7pm (BBC One)
Wednesday 11th July Winner 59 v winner 60 7pm (BBC One)
Sunday 15th July Winners of two semi-finals 4pm (BBC One)
More after the break
4K iPlayer: what you need
The trial is streaming on BBC iPlayer over the internet but you won't be able to watch on your standard web browser and computer monitor.
You'll need a compatible 4K TV. The full list of compatible 4K iPlayer TVs is here, and it includes 2016, 2017 and 2018 LG TVs, 2017 and 2018 Samsung TVs, plus TVs from Loewe, Panasonic, Philips, Sony and more. The list appears to be fluid, so it's worth keeping an eye on.
There are some notable absentees, including Samsung's 2016 TVs which, though they do support HLG, don't support DVB-DASH, the technology standard behind the BBC's adaptive streaming. Similarly, Sony's 2017 A1 OLED isn't on the list, nor are a vast chunk of Sony's 2016 and 2017 line-up.
If you have a 4K TV that isn't on the list, you do have the option of the Virgin TV V6 box, Roku Streaming Stick+ or the Sony PS4. Interestingly, there's no support for live 4K iPlayer broadcasts on Sky Q, even though the Sky Q platform supports on demand (rather than live) Ultra HD iPlayer content. We're still attempting to clarify that with the BBC.
As well as the TV, you will also need a fast enough internet connection. The BBC recommends people will need an internet connection of at least 40Mbit/s for the full 3840-pixel Ultra HD resolution, and recommends a wired connection rather than connecting over wi-fi.
4K iPlayer: picture quality
The iPlayer trial will deliver 4K and HDR video. The BBC will use the Hybrid Log-Gamma version of HDR, which the corporation invented along with Japanese broadcaster, NHK.
It promises to provide better picture quality not only to HDR Ultra HD devices, but to the vast majority of Standard Dynamic Range Ultra HD devices too. So even if your TV doesn't support HLG HDR, you should see a benefit.
The BBC is using adaptive bitrate, which means the quality of the picture will vary according to the quality of your internet connection. The highest quality is 3840 x 2160, at 50 frames per second. If your connection isn't fast enough, the picture resolution will decrease. The BBC says at 20Mbit per second you'll get 2560 resolution video, and it'll drop right down to 720p HD if required.
4K iPlayer: what's next?
So, while we're all excited to enjoy the World Cup in 4K on the BBC, we can't help but already think about what will come next and whether the BBC will continue offering 4K broadcasts on a regular basis.
The BBC has said it will be using the experience and data gathered from the trial "to optimise UHD delivery in the future". The trial will also help "the BBC and wider industry prepare for a time when delivering such large-scale events in such high quality, for larger audiences, over the open Internet is normal," said a BBC statement.
The BBC currently broadcasts FA Cup football, Wimbledon tennis, Six Nations rugby, rugby league, snooker, athletics and plenty more, as well as the Olympics. So can we expect to see them all in 4K in the future? It certainly looks much more likely now.