Google AdWords API blog has posted planned changes for 2009. It also mentions that this might be implemented in the first half of the 2009.
* New calls features o More operations in a single call: We're changing the way services are constructed so that you'll be able to accomplish more work per call. Specifically, operations will accept a variety of modifiers acting on elements across ad groups. For example, you'll be able to add, update, and delete keywords across ad groups, all within a single call.
o Asynchronous calls: We'll offer asynchronous calls, which will allow you to work with large sets of data faster and more easily. Instead of having to wait for our system to fully complete your request before you can make another one, you'll be able to make another call as soon as the API service confirms that it's received your previous call. No more waiting for large requests to be finished. (Synchronous methods will still be supported as well.)
o Partial failure acceptance: We plan to support partial failure, so large posts aren't rolled back due to a few errors. This allows you to keep moving forward with development and not have to re-do the same posts.
* Lower costs: We plan to directly reduce API units consumed for the new asynchronous methods, and are exploring other ways to improve the value you get from the AdWords API by lowering costs and/or quota use.
* Faster development: Our new codebase will allow us to expose new AdWords features faster, keeping the API more closely in line with the AdWords web interface. This will make it easier for you to keep your applications current and to take advantage of the latest AdWords advancements.
The fundamental changes are supposed to offer you some advantages:
Google AdWords
API