Last valuation was $6 billion, they initially wanted to go public in November of 2020 but because of COVID they delayed it. Doesn't sound cheap to me for a company who isn't profitable yet... (Microsoft payed 7,5 billion for GitHub and I think we can all agree that GitLab isn't used as much so nearly the same valuations seems a bit high too me)
The simplest heuristic is price/sales ratios.
Money losing companies that are doubling their revenue are currently going for nosebleed ps ratios of 40-100, which equates to $5-$13b market cap.