Cryptocurrencies are starting the week on a positive note.

Ethereum, the world’s second-largest digital coin, surged over 4% in 24 hours Monday to hit a new all-time high above $4,700. The token was last trading at a price of $4,740, according to Coin Metrics data.

Bitcoin, meanwhile, climbed 7% to a price of $66,250, inching back toward a record high above $66,900 set in late October.

The reason for the move wasn’t clear. Cryptocurrencies are known for their volatile price swings, with moves of up to 20% higher or lower relatively common.

Ethereum is a key player in DeFi. Some of the biggest DeFi services, including decentralized exchange Uniswap and lending platform Aave, run on the Ethereum network.

Still, DeFi has caught the attention of regulators lately, and experts have warned a crackdown is imminent.

Ethereum is also the backbone for many non-fungible tokens, or NFTs. NFTs are like digital receipts that keep a record of ownership for rare items like online art.

They have seen a boom in activity this year, with one token auctioned at Christie’s selling for a record $69 million.

Still, ethereum is up against some fierce competition. Rival tokens like solana and cardano have surged in price this year.

Ethereum is undergoing a major upgrade which investors hope will make the network faster and more environmentally friendly.

Bitcoin and other cryptocurrencies have been criticized for their swelling consumption of energy.

The latest step in Ethereum’s overhaul arrived late last month, when an upgrade called Altair went live.

Meanwhile, bitcoin jumped to a new all-time high of nearly $67,000 last month, following the listing of the first U.S. bitcoin futures exchange-traded fund.

Crypto bulls praised the move as another sign of growing acceptance for digital assets on Wall Street.

Alternative digital currencies often rally after significant climbs in bitcoin’s price, as investors search for returns elsewhere in the market.