There have been photos of P-8s flying the kit in test at least since April 2014 (posted one on TD) as per
"Boeing and Raytheon companies are testing the Littoral Surveillance Radar System (APS-149 LSRS) on the Boeing P-8A. The Poseidon will carry the Advanced Airborne Sensor, an enhanced version of the APS-149. Photo: Russell Hill
Boeing and the US Navy began testing an Advanced Airborne Sensor (AAS) radar system for the P-8A Poseidon maritime surveillance and anti-submarine warfare (ASW) aircraft. A series of photos, taken by Russell Hill revealed earlier this week.
The radar, developed by the Raytheon company, is a follow-on to the Littoral Surveillance Radar System APS-149"
so I guess all that's happened is that it has been rolled out (at that time the roll-out was planned for 2016) under the confirmed name APS-154
As for the RAF Sentinels, the linked NI piece quotes 2021 for retirement and I can't find any newer support contract than the one from 2016... which does expire in 2021
" contract to provide support for the aircraft for the next 5 years is expected to sustain around 120 jobs at RAF Waddington in Lincolnshire and 40 roles at Hawarden Airfield near Broughton, North Wales."
- sure. it is only a piece of paper that needs to be signed for prolonging (will only work if capacity is not run down in anticipation of the opposite)