Hi @ justin-7809，

> If AES 256 select, is the algorithm AEAD_AES_256_CBC_HMAC_SHA_256 used?

No. AES 256 is one Encryption Algorithm for backup encryption. Always Encrypted uses the AEAD_AES_256_CBC_HMAC_SHA_256 algorithm to encrypt data in the database. Refer to Data Encryption Algorithm.

Best regards,

Cathy