The Sony Cyber-shot RX100 IV (M4) is less of an clear upgraade over its predecessor the RX100 III (M3) than a forked alternative; for a variety of reasons, I'd classify it as an advanced compact for video enthusiasts rather than a straight-up advanced compact, at least until the price drops a bit.
Great video features to supplement its 4K capabilities distinguish the Sony Cyber-shot RX100 IV from the rest of the advanced-compact pack; It also retains the nice design perks, like a popup electronic viewfinder, of the earlier RX100 models
Like its predecessor; the autofocus system could be more consistent and the battery life has gotten even worse