Google announced that it is going to start making AdWords API usage free starting March 1. They're doing away with the preferred pricing model.
There will be two levels of API access once the changes take effect: basic and standard. The former will be the default, allowing for up to 10,000 operations per day. The latter will be available to qualified developers with no daily limit on operations. Neither option comes with a charge.
"If you have an approved AdWords API token and plan to execute fewer than 10,000 operations per day, there's no action needed. You're covered with basic access," says AdWords product manager S. Srikanth Belwadi.
"Based on your history with the AdWords API and details you’ve shared with us, you might be pre-qualified for standard access," says Belwadi. "If so, we will contact you within the next week and let you know. Please keep your contact email address up-to-date in the My Client Center (MCC) account associated with your developer token. If you haven’t been contacted or if you haven’t applied for standard access by February 28th 2013, your token will only have basic access starting March 1st 2013."
If you think you need standard access, you can apply for it here.
There's an FAQ section in Google's help center further discussing the changes here.