B787 First Officer reported a cargo heat fire indication and a diversion to another airport.

Narrative

At XA:00 Zulu; Day; on 2nd break; in bunk; called to cockpit for potential cargo fire/overheat; divert to ZZZZ at Location; at 30 minutes shy of Location 1. Cockpit indications are EICAS message 'Smoke UPR DR 4'; with activated smoke alarm; 30' later 'Bulk Cargo Heat'; and within a minute after tasking Flight Attendant's (FA) with checking floor temperature; they reported back that floor in area of 4R was 'extremely hot'. Captain (CA) and Relief Pilot have initiated a track offset of 5 NM (R) from track Q and heading towards ZZZZ. Quick seat change between First Officer (FO) and myself; followed by [advising ATC] on Frequency HF; all external lights on and a descent from FL400 to FL 395; and at 150 (R) degree turn towards ZZZZ. Clearance coordinated with ZZZZ [Approach] on Frequency HF direct to ZZZZ; updated to direct ZZZZZ then ZZZZ. Handed off to ZZZZ [Approach] on VHF and direct route requested and approved. Mach 0.87 selected to minimize time en-route and high speed descent requested once clear of all east bound traffic. High speed requested and approved below 10;000 ft; by ZZZZ [Approach]. Gathered weather info and NOTAMs for ZZZZ and accomplished diversion checklist with Relief Pilot. Relief Pilot made PA to passengers and accomplished [briefing] with FAs. Maintained 350 kts until 25 NM prior to ZZZZZ1. C/F/R assistance requested with ZZZZ Approach upon landing. Briefed RNAV Runway XX with Captain. Executed approach and landing to full stop on runway with touchdown at XB:06 Zulu; VFR conditions; 50 NM visibility; extremely dark. Passengers advised to remain in their seats by Relief Pilot; cargo doors opened by C/F/R and an initial inspection accomplished on runway with engines running. After initial all clear by C/F/R taxied clear of runway with emergency vehicles following to parking spot near aviation ramp. Engines shutdown; passengers advised to remain in their seat as a 2nd thorough inspection is accomplished by C/F/R. No facilitation for passenger at ZZZZ available and passenger remain on aircraft along with crew for 6 hrs until deplaning to relief flight from ZZZ. Thorough debrief accomplished between pilots; FA's; ground crew. Outstanding leadership/CRM facilitated by Captain during entire event. Deplaned aircraft and proceeded to hotel after all passengers boarded onto recovery aircraft 6.5 hrs after landing. Captain worked with Chief Pilot; Dispatch; In-flight Service; maintenance; ZZZ1 [Chief Pilot] and multiple agencies for the successful execution of the recovery of the aircraft to ZZZ1.