TLDR: Originally 6 out of 6 cables failed diagnostics. I returned all 6 cables to Cable Matters. Cable Matters sent me 3 new cables for free and told me to test again. 2 cables still failed (I didn't test the 3rd one). I reached out to Denon support for my AVR-X4700H receiver, who provided ZERO help because they said they didn't support the HDMI diags for end-users. Cable Matters sent me videos of their passing tests in their lab with their identical Denon receiver, and advised me to hard power cycle my receiver before entering the HDMI diag menu. This worked and now the 2 cables I tested prior are now passing 40Gbps 8k diagnostics every time. So thanks to Cable Matters for reaching out to by phone and email since they were very concerned with this review, and wanted to get down to the bottom of it. No thanks to Denon support......Original Comment:I bought 2 packs of these "8k, 48Gbps" cables, and connected all 6 of them to my Denon AVR-x4700h receiver's built-in 8k HDMI diagnostic and every single one of them failed the 8k portion of the test. I sent all of them back for a refund. Avoid Avoid Avoid! Save your money and buy REAL 8k CERTIFIED cables. Oh wait, there are no cables on the market right now that have official Ultra High Speed certification yet. That basically means all current 8k cables on the market right now are sold by scammers who get around the issue by telling you "we tested them" which means literally nothing, and/or also offering refunds. I'd wager that most people who are buying 8k cables right now don't have the proper testing equipment to verify their uncertified cables, and are just using them primarily for 4k content and think they might be future proofing their video resolution needs, but guess what? Those people are getting scammed....Update: 8/31/2020Cable Matters support has reached out to me to claim that they have multiple Denon AVR-x4700h receivers at multiple labs from which they're seeing passing test results of their own cables through the Denon's built in diagnostics. They have also sent me a free pack of new 8k cables and requested that I test again. I did another test with at least one of the new cables, and received inconsistent, but mostly failed results, again. I have browsed around the internet and have found other instances of owners of the same Denon receiver who are experiencing very inconsistent test results for other 8k cables from other brands. So either Denon's receiver is having a problem performing these tests consistently, or these uncertified cables are indeed snake oil. To be fair to this seller, and as objective as possible, I've reached out to Denon's support to see if there are any known issues with 8k HDMI testing. I've raised my rating to 3 stars until I hear back from Denon, and will provide further updates.Update 9/1/2020Spoke with Denon's end-user support who were of ZERO help because they say that the HDMI diagnostic features aren't something they support for end-users, but only installers and repair partners etc.. So I took Cable Matters advice and did a hard power-cycle of my Denon receiver before entering the HDMI cable diagnostics menu. This ended up working, and I am now getting 100% passing results over-and-over between a few cables that they sent me as freebies. I also connected 2 of my old HDMI cables right after and 1 of them faled past 18Gbps, and the other passed at 40Gbps, which is strange, but hey, i'll take it, for now. I've updated my rating to 5 stars since I have no other means of testing outside of my receiver, and since Cable Matters helped me troubleshoot by using their own receiver in their lab, and sending me videos of their passing results. I still have to advise that unless you're buy certified cables, there is no guauruntee they'll perform at the level a seller claims unless you have the ability to test it with the proper content and compatible gear.