Tether is tightening its grip on Twenty One Capital (XXI), the Bitcoin treasury firm it co-founded last year, by buying out SoftBank's entire stake in the venture.

The stablecoin issuer acquired 89.1 million shares from the Japanese tech giant, according to an SEC filing. While the terms were not disclosed, SoftBank likely took a loss: the position was recently valued at roughly $711 million, down from the nearly $1 billion it paid last June.

XXI stock is up 5% on the day, giving it a $5.2 billion market cap. But shares remain 83% below their all-time high of $53, reached last year amid a wave of Bitcoin-buying firms hitting Wall Street.

Tether CEO Paolo Ardoino said the buyout underscores the company's conviction in the venture, calling SoftBank's involvement a stamp of credibility. XXI holds 43,514 Bitcoin, worth about $3.4 billion at current prices.

SoftBank's exit also triggered the immediate resignation of its board designees, leaving XXI temporarily non-compliant with NYSE audit committee rules. The firm said it will appoint a new independent member "as soon as practicable."