$3m-$4m a month.
In a large round, everyone is going to get nervous if it can’t (x) in practice last 24 months and (y) in theory, last forever. Everyone in a large round wants to believe the company, worse case, won’t have to raise again pre-IPO.
$3m-$4m a month for now, with the potential to slowly ratchet that down in a year if the plan comes up a bit short, gives you a lot of runway with $100m.
Some will spend much less, and hold onto it for a warchart. A handful will spend more ($5m+) and go for broke. It’s not uncommon for a start-up at this phase to burn $50m or even $100m a year before IPO’ing (although then, of course, you need to raise more than $100m!).
But a late stage round should last 24+ months, with a chance to stretch out far long worst-case, to make everyone comfortable.