The v201601 release of the AdWords API included a new optimizeOnEstimatedConversions attribute of Customer.conversionTrackingSettings that allowed you to opt-in to including cross-device conversions in the Conversions column. With this option set to true, AdWords includes cross-device conversions when optimizing for conversions in an automated bid strategy.

What's changing

• Starting on August 16, 2016, new AdWords accounts will automatically have optimizeOnEstimatedConversions set to true.
• During September, 2016, the optimizeOnEstimatedConversions setting will be changed to true on all existing AdWords accounts to give you the most complete view of performance possible.
• Starting on September 6, 2016, the optimizeOnEstimatedConversions field in the AdWords API will become read-only. If your CustomerService mutate request attempts to modify this field by sending a value other than the current value, the request will fail with RequestError.INVALID_INPUT.

For more information, check out the recent Inside AdWords blog post on cross-device conversions.

What you should do
Prior to September 6, 2016, ensure that your CustomerService mutate requests do not attempt to modify the value of optimizeOnEstimatedConversions. You can also migrate your accounts before the migration by setting optimizeOnEstimatedConversions to true.

If you have any questions, please post on the forum or the Ads Developers Plus Page.

- Josh Radcliff, AdWords API Team

Source: Google Ads Developer Blog