No negotiation is required. The policy is 'we don't track vacation days' and that would be just as true for you looking for 10 weeks as it is for me who took 4. I'm not a benchmark-setter (or follower) I just happened to take 4 weeks so that's what I shared.

That said, you can't expect it to be considered in a vacuum. If you want to take 2.5 months of vacation, your work does need to be unimpeachably strong, and your dedication needs to be obvious to your teammates.