I've been involved in many startups, and this type of fundraising is not common, or at least it wasn't common before a few years or so ago
The whole concept of talking about "runway" is basically calculating how much cash in the bank, that is actually in your bank account, will last. And this arrangement is different, as there are contingencies. In the past, VCs would just give you money in a particular series, and then if your business did well, they'd eventually give you more money in a later series. But it wasn't like they announced it all up front in, say, a Series A, but a big chunk of the money would only be delivered if you met milestones.
The whole concept of talking about "runway" is basically calculating how much cash in the bank, that is actually in your bank account, will last. And this arrangement is different, as there are contingencies. In the past, VCs would just give you money in a particular series, and then if your business did well, they'd eventually give you more money in a later series. But it wasn't like they announced it all up front in, say, a Series A, but a big chunk of the money would only be delivered if you met milestones.