android GCM registration ID max length

In Google Cloud Messaging, what is exactly the registration ID maximum length?

What is GCM registration ID?

A Registration ID is an identifier assigned by GCM to a single instance of a single application installed on an Android device. The device is assigned this identifier when it registers to Google Cloud Messaging. The GCM documentation doesn't specify what information is encoded in this identifier.

What is GCM and how it works?

GCM stands for Google Cloud Messaging. Every push notification receive on any Android device is sent by the GCM only. when sender sends an push notification then it goes to GCM. GCM receives that push and forward it to particular Android Device by its Unique device id.

~~A google engineer said the registration ID can be up to 4K~~. Users have observed it is 255 characters.

i think i can help you out with this... i´m working with GCM this week, and my device´s registration ID looks like this:

APA91bHPRgkF3JUikC4ENAHEeMrd41Zxv3hVZjC9KtT8OvPVGJ-hQMRKRrZuJAEcl7B338qju59zJMjw2DELjzEvxwYv7hH5Ynpc1ODQ0aT4U4OFEeco8ohsN5PjL1iC2dNtk2BAokeMCg2ZXKqpc8FXKmhX94kIxQ

163 characters!

i hope this can help you out...