16.1.9 JSON Format for ACLs
ACE flags and masks are members of a 32-bit quantity that is widely understood in its hexadecimal representations. The JSON data format does not support hexadecimal integers, however. For this reason, all hexadecimal integers in CDMI ACLs shall be represented as quoted strings containing a leading "0x".
"cdmi_acl" : [ { "acetype" : "0xnn", .....
If readability by humans is paramount, then why not use a bit string, like in ls(1)? If readability is not an issue, just transmit decimal.
They also have hexadecimals without "0x" prefix elsewhere in the spec.