Firmware G998U1UEU4AUF5 is out now for unlocked S1 Ultras in the US (no new security patch, still Jun 1). It's downloadable via Frija (CSC: XAA) if not yet available OTA from your carrier. The bootloader-number increment (from 3 to 4) implies that once you upgrade to AUF5, you no longer have the option to downgrade to an earlier firmware version.
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