Comparison review of Samsung Q9FN vs Q90R vs Q900R in the 65-inch class (QN65Q9FNAFXZA vs QN65Q90RAFXZA vs QN65Q900RBFXZA), 75-inch class (QN75Q9FNAFXZA vs QN75Q90RAFXZA vs QN75Q900RBFXZA), and 82-inch class (QN82Q90RAFXZA vs QN82Q900RBFXZA).
The biggest difference between the Samsung Q900R vs Q90R (and Q9FN) is arguably the resolution since the Q900R is an 8K TV with a resolution of 7,680 x 4,320 pixels while both the Q9FN and Q90R are 4K TVs, meaning their resolution is 3,840 x 2,160 pixels. As a result, even the 98-inch class Q900R, which is the largest screen in the Samsung 8K QLED series, has higher pixel density than the 65-inch Q90R and Q9FN, for example (and the 65-inch class Q900R has about twice the pixel density of its 4K counterparts of the same size). Specifically, the 98-inch class Q900R (97.5 inches diagonally) has ~90 PPI (Pixel Per Inch); the 85-inch class Q900R (the diagonal measurement is 84.5 inches) has ~104 PPI (Pixels Per Inch); the 82-inch class Q900R (81.5 inches diagonal measurement) has ~108 PPI (Pixels Per Inch); the 75-inch class Q900R (74.5 inches diagonally) has ~118 PPI (Pixels Per Inch), and the 65-inch class Q900R (64.5 inches measured diagonally) has ~136 PPI. In contrast, the 65-inch class Q9FN and Q90R have ~68 PPI (Pixels Per Inch), and the 75-inch class 4K models have ~59 PPI. The benefit of the 8K resolution is therefore not only limited to providing sharper image (when TVs of identical size are compared), but also that you can upgrade to a considerably bigger TV while keeping your current viewing distance the same, without having to worry that the picture may become pixelated. In fact, it's quite the opposite since even if you switch from a 65-inch TV with 4K resolution to a 98-inch TV with 8K resolution, there will still be increase in sharpness (by approximately a third in terms of PPI).
Although full-array backlight is used with both 4K and 8K resolution QLED TVs, the denser pixel structure on the Q900R necessitates more powerful backlight than Q9FN and Q90R have. As a result, the Q900R in the 75-inch class and above is able to show small specular highlights in HDR content approximately twice as bright as the Q9FN and Q90R. Specifically, the Q900R in the 75-inch, 82-inch, 85-inch, and 98-inch size class has a Quantum HDR 32x index which translates to about 4,000cd/m2 with low-APL (Average Picture Level) content in HDR mode. The Q9FN and Q90R, on the other hand, are able to reach approximately 2,000cd/m2 in the same set of conditions. Additionally, there is no difference between screen sizes in the Q90R range since the 65-inch, 75-inch, and 82-inch class all have a Quantum HDR 16x index, meaning their backlight have identical luminance output. As previously mentioned, the power of the backlight in the Q900R series varies with the screen size. The 65-inch class Q900R has lower peak luminance output than its counterparts in the 75-inch class and above. That being said, it's still higher than either the Q9FN or Q90R because the 65-inch class Q900R has a Quantum HDR 24x index, meaning the peak brightness in small specular highlights is approximately 3,000cd/m2. This allows the 65-inch Q900R to completely avoid tone-mapping with HDR content that is mastered to 1,000cd/m2, and given its 100% DCI-P3 Color Volume, most HDR content can be displayed without any compression of the dynamic range or reduction of color saturation. The same applies to the remaining size classes in the Q900R series, as well as the Q9FN and Q90R TVs because they all utilize quantum dots for the purpose of optimizing the spectrum of the backlight, and producing narrow peaks in the red, green, and blue spectral regions. The pure primary colors is what allows the QLED TV to reach 100% DCI-P3 color volume. When HDR content is mastered to 4,000cd/m2, however, only the Q900R series in the 75-inch class and above are able to avoid compression of the dynamic range whereas the Q9FN, Q90R, and the 65-inch Q900R resort to using some tone-mapping, albeit minimal, especially the 65-inch class Q900R (due to its higher peak brightness than the Q9FN and Q90R). The Samsung QLED TVs support HDR10+ format which, unlike the HDR10, uses dynamic metadata so that content can be optimized on scene-by-scene basis, or even frame-by-frame, meaning that unnecessary compression of dynamic range can be avoided when, for example, the scene has no highlights. As a result, the overall brightness of mid-tones with HDR10+ content is on par between Q9FN, Q90R, and Q900R. When highlights are present, though, the Q900R series has an advantage over either Q9FN or Q90R, albeit it can be observed only when the HDR content is mastered to 4,000cd/m2. The three Samsung QLED TVs also support HLG (Hybrid Log Gamma) content but are not compatible with Dolby Vision.
The Q90R is equipped with Quantum 4K processor while the Q900R utilizes Quantum 8K processor which is understandable since the former needs to upscale only to 4K (which is its native resolution) whereas the Q900R have to be able to upscale lower resolution content to its native resolution of 8K. The upscaling algorithms in both cases, however, are AI-generated. For that, one database with low resolution and quality samples is used, and another containing their corresponding high resolution and quality versions. The difference between the two is what the automatically generated upscaling algorithms are based on, hence the AI-upscaling capability on the Q900R and Q90R. The Q9FN uses different processor: the Q Engine, so it doesn't have any AI-upscaling capabilities. Furthermore, the Q9FN omits the machine learning techniques of the Q90R and Q900R so it's not able to produce improved upscaling results over time. The Quantum processors on the Q90R and Q900R are able to optimize video black level, brightness, and image depth depending on the scene, meaning they don't need a dedicated SDR-to-HDR upconversion mode, unlike the Q9FN which has to be in the HDR+ mode if you want SDR content to appear more HDR-like.
There is an optical layer on the Q90R and Q900R for the purpose of providing Ultra Viewing Angle, meaning that unlike the Q9FN, the Q90R and Q900R are able to prevent the image from being washed-out during off-axis viewing. Even though there is no significant raise in the black level (or color saturation loss) as you move from the center to the sides, it should be said that the on-axis black level (without local dimming) on the Q90R and Q900R is not as deep as on the Q9FN because of the optical layer. Nevertheless, by virtue of having a local dimming system that is just as capable as the Q9FN's, the Q90R and Q900R are able to largely compensate for the effect that optical layer has on their minimum luminance level. The optical layer also affects how reflections appear, despite the identical anti-reflective filter on three Samsung QLED TVs. The reflections on the Q90R and Q900R appear dimmer (due to being more diffuse) while they are brighter on Q9FN since are more concentrated.
The Q90R and Q900R work with Amazon Alexa and Google Assistant but you'll need another device (e.g. Amazon Echo or Google Home, both of which are sold separately) since the Samsung QLED TVs don't have these voice assistants built-in. They do include Bixby, though, which is developed by Samsung, and can be used for controlling the TV with voice commands, and answering certain queries. The Q9FN also relies on Bixby for voice commands using the built-in microphone in the One Remote but you need to press and hold the microphone button as you speak which is slightly less convenient than having a dedicated smart speaker. The Q90R and Q900RB address this issue by having far-field voice capabilities, meaning the microphone in the One Remote is able to pick voice commands directed at Bixby from slightly longer distances (without having to press and hold a button). That being said, there is still a Microphone button on the Q90R and Q900RB's remote, in case if you wish to use Bixby this way. The Samsung One Remote included with the Q90R and Q900RB has dedicated buttons for Netflix, Amazon Prime Video, and Hulu, meaning that you have a quick way to launch these apps whereas the Q9FN's remote omits these three buttons.
There is no upgrade in terms of codec support on the Q900RB (65-inch, 75-inch, 82-inch, and 98-inch class) and Q90R in comparison to the last year's Q900RA (85-inch class) and Q9FN. For example, with 4K-resolution files, they all support HEVC Main and Main 10 profiles up to level 5.1, meaning up to 60fps and 80MBps bitrate, so neither of them is able to decode 4K@120fps files. In other words, they are not compatible with 4K HFR (High Frame Rate) content via USB or streaming apps. It should be said, though, that the Q90R and Q900RB are able to accept 4K@120Hz signal on one of their HDMI inputs (HDMI 4) on the One Connect Box, provided color bit depth doesn't exceed 10-bit, and 4:2:0 chroma subsampling is used (the latter applies only to the Q90R since the Q900RB supports full 4:4:4 chroma resolution with 4K@120Hz, except for the 85-inch class model which was released in 2018). The HDMI 4 input on the Q90R and Q900RB also has an advantage over the Q9FN's HDMI inputs (which are also located in the One Connect Box) when it comes to 10-bit 4K@60Hz signals because it can accept full chroma resolution in that case whereas the Q9FN's HDMI inputs are limited to 4:2:2 or 4:2:0 chroma subsampling with 10-bit 4K@60Hz feeds. There are some differences specific to the 8K QLED Samsung TVs, such as the last's years Q900RA (85-inch class) being able to accept 7680x4320 signal only up to 30fps (8-bit or 10-bit color depth; 4:2:0 chroma subsampling) whereas the current Q900RB models (82-inch class and below, and the 98-inch class) are compatible with full chroma resolution 8K@30Hz signals (8-bit or 10-bit color depth), and more importantly: 8K@60Hz signal (4:2:0 chroma subsampling, 10-bit color depth), albeit only on the HDMI 4 input. HEVC 8K decoding on the Q900RB is supported up to level 6.1 (Main and Main 10 profiles), meaning a maximum of 60fps and 100MBps bitrate. The VP9 decoding capabilities are limited to 3840x2160 at 60fps, even on the 8K Samsung QLED TVs.