Last October, 
we announced the 
sunset of accelerated budget delivery for use with Search campaigns, Shopping campaigns, and shared budgets. These campaigns have since been made unavailable for use with accelerated budget delivery.
Later this year, accelerated budget delivery will also be sunset for all other remaining campaign types for both shared and non-shared budgets. This includes Display, App, video campaigns, and others, and this sunset will affect budgets in all versions of the AdWords API, Google Ads API, and Google Ads scripts.
Starting at the 
end of April, 2020, scripts and both APIs will prevent campaigns from using new and existing budgets with the 
ACCELERATED delivery method.
  - Creating a new budget with its delivery method field set to ACCELERATEDwill no longer be allowed.
- Changing an existing budget from STANDARDtoACCELERATEDdelivery method will no longer be allowed.
- Setting a campaign to use a pre-existing budget with an ACCELERATEDdelivery method will no longer be allowed.
Any of the above operations will result in errors from the APIs and scripts, according to the following:
AdWords API
Google Ads API
Google Ads scripts
Making changes to existing 
ACCELERATED budgets (e.g., updating 
amount or 
status fields in the API, or using their corresponding 
AdsApp.Budget methods in scripts) will still be allowed 
until May 2020, after which any modification to these budgets will also result in analogous errors.
Future versions of the Google Ads API and Google Ads scripts may remove support for the accelerated budget delivery option altogether.
Please don’t hesitate to reach out to us on the 
AdWords API / Google Ads API forum or the 
Google Ads scripts forum if you have any questions about this change.
Adam Ohren, Google Ads API Team