Are IRA distributions subject to Generation Skipping Tax (GST)?

Sec. 26.2611-1 Generation-skipping transfer defined.

A generation-skipping transfer (GST) is an event that is either a
direct skip, a taxable distribution, or a taxable termination. See Sec.
26.2612-1 for the definition of these terms. The determination as to
whether an event is a GST is made by reference to the most recent
transfer subject to the estate or gift tax. See Sec. 26.2652-1(a)(2)
for determining whether a transfer is subject to Federal estate or gift
tax.

yes. The GST tax applies to a transfer of property that skips a living member of one or more an invervening generations, e.g. GChild inherits IRA of Gfather while GChild's parent (father) is alive. GST would not apply if father was dead at time of transfer. However, there is a life time exemption of 2.0M on GST transfers plus 12,000 annual exemption.