SpaceX is the biggest rising star of all time, refinancing $17.5B of high-yield debt at 12% coupons to a $20B facility at 4.6%, making it effectively net debt zero with an IG rating.
With a market cap of ~$2T and only $20B in debt (1% of EV), plus >$80B cash, SpaceX has no net debt and is clearly IG-rated.