I have a former colleague that on looking for a new role was offered "unlimited vacation". He asked what the limit was. "Unlimited", they replied. "Honestly?",

I have a former colleague that on looking for a new role was offered "unlimited vacation". He asked what the limit was. "Unlimited", they replied. "Honestly?", he ventured. "Yes, unlimited". "OK, then", he said, "I'd like to book the entire year off". "Oh no, you can't do that!", they replied. "I thought so. So what's the limit?", he asked again. "There is no limit", they replied. "But you just said I couldn't have a year off", he pointed out. "It has to be reasonable", they said. This went back and forth. In the end "unlimited holiday" in the UK for this firm was 28 days. That is the statutory legal minimum in the UK. If he went over this, it would likely be accepted at the time, but "noticed" in performance/salary reviews, etc. So, in short, unlimited vacation is a con, and you should try the above yourself. It'll lead to an interesting conversation, although it may harm your chances of getting an offer if you time it wrong.