Starting soon, any contacts that have an "address line 3" submitted through the API will see that field ignored. As a company, we're optimizing contact data to be in line with the usage that we see from our customers. Address line 3 has already been removed from the interface your see when you login to an account. Our goal is to keep what you see in an account in line with what our API does.
As we build out the next version of our API, we're adding fields that our customers have more use for, like more custom fields, birthdays, and anniversaries.
Thank you for being our valued accountholders & developers, and please feel free to give feedback here for fields and functionality you'd like to see in the future.