In stock again, though not the lowest it has been ($3599.40). Good price if you're after big OLED.
Below taken from @ozzbargainer's post
rtings
The Samsung S90D/S90DD OLED is marginally better than the Samsung S90C OLED. The S90D is a bit brighter in HDR, so highlights in HDR content stand out a little bit more, and it has better color volume, so it can display very bright colors a bit better. The S90D also has slightly better processing, so there's less banding in colors, and it does a better job with smoothing out low-quality content.
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great price for the 90D series