Air carrier Captain reported temporary GPS navigation anomalies during cruise.

Narrative

Approximately 200 miles past Japan entering Pacific oceanic airspace; GPS updating stopped (No GPS on NAV screen; POS REF page 2/3 blank). EICAS message ADS-B OUT L appeared.Per flight manual (FM) selected right transponder. No further EICAS message.We watched as the ANP started to slowly creep up. About .1 increase every couple of minutes. But it never got above 3.4 until about 2 hours later. It then went as high as 4.4.After the ANP crept up above 2.0; contact was made with Dispatch and Maintenance Control. After confirming all circuit breakers in; clock working; and no other abnormalities; we were instructed to continue; but to inform if it went above 10.I have read about spoofing and interference in the Middle East; but did not expect this over the Pacific. We contacted several other aircraft in the area and confirmed that we were the only ones with this issue.Weather radar appeared to work fine; though it was mostly clear that night. And our iPads and apps seemed unaffected.It was like being in the old 747-100 with some Inertial Navigation System (INS) drift. I didn't suspect spoofing or jamming based on where we were operating. And while we had some degradation being displayed like increasing ANP and no GPS signal present; other things worked fine; like the clock; weather radar and EFB apps. We also never got an EICAS for GPS L or R. ATC agreed to keep them informed if ANP approached 10 or greater.GPS never came back. We also attempted selecting OFF for RAD NAV INHIBIT; but as expected over the Pacific that did not help. ELB entry was made.Weather was scattered at ZZZ and a successful ILS approach/visual to Runway XXR was conducted.