Gulfstream pilot reported diverting to an alternate airport after experiencing a cracked front windshield.

Narrative

On the ground at ZZZZ; I looked at the flight plan & noted the route to PIC Person A. He didn't indicate any issues with the route. We took off from ZZZZ. I had no firsthand experience with HF radios so Person A was assisting with radio communications. At FL430 while in cruise; the left front windshield cracked. We had FL450 as our optimal cruise altitude at the time. Person A was flying the airplane; and handling the radios- we were on HF; over 500 miles out from land. We were flying from ZZZZ; and had over 8000 lbs of fuel on board at the time. ATC gave us FL390 immediately; we asked for FL240- they denied us due to traffic; and asked if we wanted to declare an emergency. We said no; not at this time since pressurization and the crack seemed stable at the time. The checklist called for FL350 or lower- ATC gave us FL350; and we put our masks on during the descent in the event of decompression. They held us at FL350; and we were still on HF. ATC continued to deny lower altitude due to traffic. No issues with pressurization or the crack growing in size. I read the checklist out loud- confirmed the correct circuit breaker for left front window heat. In order to bring cabin differential pressure down to 7.5; I raised cabin altitude via cabin altitude selector window. ATC continued to hold us at FL350 which was okay since the checklist called for FL350 or lower; and pressurization seemed stable. We continued our descent from FL350-14;000' and it reached above 9500' cabin altitude; and we got a CABIN ALT HIGH red Crew Alerting System message before I switched the cabin pressurization from FLIGHT to LANDING auto mode. We requested priority handling and continued down below FL180. We leveled off; and pressurization stabilized. We landed at ZZZ safely.