tvOS 12.3 (build 16M5139a) is an official Apple over-the-air update for the Apple TV 4 (2015), released on 2019-04-22T17:08:28Z. The update package is 1.37 GB. This is a full OTA update that can be applied from any compatible base version. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c90fcde83dfce75b1b05df4da32be1f3ecef3ee1.zip.