This post compiles all known OTA updates for the Nexus 6.
Nexus 6 (shamu XT1100 and XT1103) - shamu
Current firmware: Android 5.0.1, Build LRX22C
LRX22C from LRX21M
LRX22C from LRX21O
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LRX21O from LNX07M
Credits: oldblue910