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 optimizeOnEstimatedConversionsset totrue.
- During September, 2016, the optimizeOnEstimatedConversionssetting will be changed totrueon all existing AdWords accounts to give you the most complete view of performance possible.
- Starting on September 6, 2016, the optimizeOnEstimatedConversionsfield 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
 -  Josh Radcliff, AdWords API Team