Bitcoin doesn’t have a future as a payments network, according to Sam Bankman-Fried, founder and chief executive at crypto exchange FTX and one of the most high-profile executives in the crypto industry.

Bankman-Fried said that the proof-of-work system, which bitcoin BTCUSD, -4.41% was built on to validate blockchain transactions, wasn’t capable of being scaled up to deal with millions of transactions, according to the Financial Times.

“The BTC network can’t sustain thousands/millions of TPS (transactions per second),” although bitcoin can be transferred on other blockchains layered on top of the original one, such as the Lightning network, Bankman-Fried tweeted on Monday.

“Things that you’re doing millions of transactions a second with (will) have to be extremely efficient and lightweight and lower energy cost. Proof of stake networks are,” Bankman-Fried told the Financial Times.

Proof-of-stake is another mechanism to validate transactions, which consumes less energy. Ethereum ETHUSD, -5.64% is transitioning from proof-of-work to proof-of-stake.

Still, bitcoin has potential as “an asset, a commodity and a store of value,” Bankman-Fried told the Financial Times.

Bitcoin has dropped more than 55% from its all-time high in November to below $30,000 on Monday, according to CoinDesk data. Ether is down more than 58% from its record high to around $2,000.

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