In the upcoming Google App Engine 1.8.1 release, the Datastore default auto ID policy in production will switch to scattered IDs to improve performance. This change will take effect for all versions of your app uploaded with the 1.8.1 SDK.
You can try out the new behavior in the development application server, where scattered auto IDs are the default. These IDs are large, well-distributed integers, but are guaranteed to be small enough to be completely represented as 64-bit floats so they can be stored as Javascript numbers or JSON. If you still need legacy ids for some entities (e.g. because you want smaller numbers for user-facing ids), we recommend you use the allocateIds() API, which will continue to behave as before. You can also override the default auto id policy by setting the new auto_id_policy option in your app.yaml/appengine-web.xml to legacy, but please note that this option will be deprecated in a future release and will eventually be removed.
-Posted by Chris Ramsdale, Product Manager
You can try out the new behavior in the development application server, where scattered auto IDs are the default. These IDs are large, well-distributed integers, but are guaranteed to be small enough to be completely represented as 64-bit floats so they can be stored as Javascript numbers or JSON. If you still need legacy ids for some entities (e.g. because you want smaller numbers for user-facing ids), we recommend you use the allocateIds() API, which will continue to behave as before. You can also override the default auto id policy by setting the new auto_id_policy option in your app.yaml/appengine-web.xml to legacy, but please note that this option will be deprecated in a future release and will eventually be removed.
-Posted by Chris Ramsdale, Product Manager