An application programming interface (API) is an interface implemented by a software program to enable interaction with other software, similar to the way a user interface facilitates interaction between humans and computers. APIs are implemented by applications, libraries and operating systems to determine the vocabulary and calling conventions the programmer should employ to use their services. It may include specifications for routines, data structures, object classes and protocols used to communicate between the consumer and implementer of the API.What this all means from a practical standpoint is that all of the programs using this mode of connecting to the New FamilySearch database are forced to rewrite their code to reflect the changes. The fact that the API would change has been known for some time and was one of the topics of conversation at the Mesa, Arizona Family History Expo. 29 March 2010 is the date of implementation of the changes and many of the software developers, including RootsMagic, Legacy Family Tree, Ancestral Quest, Family Insight and others, have either already implemented software updates to reflect the change over or will do so in the next day or so.
If you do not upgrade, you will no longer be able to connect to New FamilySearch. I have not seen any charges for the upgrade except with Ohana Software's FamilyInsight. I was notified of the change to the API from Ohana but when I went to make the upgrade I was further notified that my one year license had expired and I would need to purchase a new license for $15.00, almost the cost of the new program. In other words, I now have a program that does not work and will have to purchase a new one from the software vendor. This is not a situation where the upgrade merely adds functionality, this is an upgrade that makes the program work. As far as I can tell, all of the other software vendors, RootsMagic, Ancestral Quest, Legacy Family Tree and others, are offering free upgrades.