Fujifilm says the X-T4 is intended as a sister model to the X-T3 rather than a direct replacement, but there are enough differences between the two that some users might wish to upgrade. And there may be people looking at the X series afresh, wanting to know which is the better choice.

The more I’ve used the X-T4, the more I believe some stills-only photographers will appreciate it

Initially I wrote that the majority of benefits would be experienced by video shooters but the more I’ve used it, the more I believe some stills-only photographers will appreciate the newer model.
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https://www.dpreview.com/articles/0751097252/fujifilm-x-t4-vs-x-t3-which-should-i-buy-and-is-it-worth-upgrading