This weekend I'll be arriving at T6 on CO early afternoon and departing to Sydney (QF) out of TBIT at 10:30pm. I'd like to spend most of the ~8h layover in the T6 CO PC and am wondering if there is a way to get to TBIT airside.

Qantas operates an airside shuttle from T4 to TBIT, so if I can get from T6 to T4 it seems I should be able to make the trip without leaving and re-clearing security. So I suppose the main question is - Is the tunnel from T6 to T4 open?