Cryptocurrency operator Circle Internet Financial said on Thursday it was valued at $9 billion under new deal terms with Concord Acquisition Corp, a blank-check firm backed by former Barclays boss Bob Diamond.

The Boston-based company said it had terminated an earlier merger agreement with Concord, which had valued Circle at $4.5 billion.

Shares of Concord, a special purpose acquisition company (SPAC), were down nearly 3% at $10.20 in premarket trading.

Circle said it had amended the deal terms as its financial outlook and market share had improved, especially in USD Coin (USDC), a stablecoin cryptocurrency whose value is directly pegged to the US dollar.

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The company is the principal operator of USDC, which has a nearly $52.4 billion market capitalization according to crypto data provider CoinGecko.

USDC's circulation has more than doubled since the original deal was announced, Circle said.

Stablecoins have soared in popularity as they offer more price stability compared with more mainstream peers like bitcoin and ether that have seen wild price swings in the past year.

Circle's new deal is an outlier in the broader SPAC market, which has seen several proposed mergers collapse in recent weeks due to unfavorable market conditions and waning investor sentiment.

SPACs are shell companies that raise money in an initial public offering, to merge with a private company and take it public. Concord raised $276 million in its IPO in December 2020.

The deal is expected to be completed by the end of the year, but can be extended to Jan. 31, 2023, under certain circumstances, Circle said.