Coinbase’s national trust company has won final approval to open, a step that puts its custody operations inside a federal supervisory framework while lawmakers in Washington press regulators to explain how such charters are being justified.

The company said on Nov. 9 that the Office of the Comptroller of the Currency had cleared the charter to begin operating. The OCC had issued preliminary conditional approval in April, a stage that signaled openness to a federal path but did not by itself permit the business to launch. Final approval is the step that typically allows a charter to be put into full use.

For Coinbase, the shift is more than a procedural milestone. A trust charter gives a custody business a single federal structure…