4k video streaming is available on Magenta Max and Go5G Plus plans for in-market plans.  

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However, be aware that when active streaming 4k UHD video will use data much faster.  If your plan has  a 50GB heavy-user threshold or a hotspot data threshold, you’ll reach them much quicker with deprioritization or throttling for the remainder of your month (provided your getting speeds capable of supporting 4K UHD).