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You cannot comment after the post's payout now. Note that, there is a second, 30 days payout in the system.

But with the HF proposal to make final payouts after 7 days - there will no longer be a 30-day second payout, right? So if the comments payouts are separate, they would also have final payout at 7 days. I'm assuming that no new comments would be allowed after original post payout then, but have not seen any wordage about it.

@merej99 (nesting limit)

Yes, after HF17, only one 7 days long payout period remains.

Since comments count as individual posts in the new system (as you have said, they have separate payout window), I don't see any reason why we shouldn't allow comments after the posts payout.