Historically, TLS used AES ciphers based on a flawed CBC-mode-based construction. These ciphers are fragile and very difficult to implement securely. TLS 1.2 added better ciphers based on AES-GCM. We current support AES_128_GCM, but many servers order by key size above all else, placing the legacy AES_256_CBC above our preferred AES_128_GCM. To simplify server configuration and negotiate modern ciphers with more existing servers, we'll be adding AES_256_GCM as well.