What is the difference between a CBDC and a stablecoin?

A central bank digital currency is a direct liability of the central bank, carrying the same credit standing as physical cash. A stablecoin is a liability of a private issuer, backed by reserves that issuer holds and manages. The distinction is credit risk: a CBDC has none in its own currency, a stablecoin has as much as its issuer and custodians carry. This is why supervisors treat reserve attestation and custodial concentration as the central questions for stablecoins and as irrelevant for a CBDC.