Holders of Zcash's original shielded pool are running out of time: about 12,200 ZEC, worth roughly $16M, still sits in Sprout as the NU7 network upgrade approaches activation at block 3,543,405.

Roughly 10,000 ZEC left Sprout over the past week, but only about 40 coins moved out on Wednesday.

Under ZIP 2003, NU7 stops accepting version 4 transactions, the only format that can spend Sprout funds. The coins are not burned, and a future upgrade could restore access, but no such path is scheduled. Sapling and transparent balances are not affected.

NU7 also cuts Zcash's target block time from 75 seconds to 25 seconds. Sprout launched in 2016 and was built on an earlier, more complex version of the network's privacy technology.