Can I be sure that all incoming apikeys are 32 alphanumeric characters?

[#1]

Sometimes we pass API keys to our backend servers rather than removing them at the Apigee level, so that we can do logging, correlation, etc.. For security and usability reasons, we always want to be sure our backends are acting upon valid input. This the incoming API key has to be validated on arrival

Can I always be sure that my client's API keys will contain 32 characters from the set [0-9,A-Z,a-z]?