Arnold Schwarzenegger -- Maria's Still Very Lunchable

Arnold Schwarzenegger hooked up with Maria Shriver at a fancy hotel Thursday ... but it's not what you think.

The former governator celebrated his 68th birthday with his estranged wife and their two daughters, Katherine and Christina, at the Montage in Bev Hills.

It's good to know they're getting along during the divorce process .... which has been ongoing for 4 years.

It's hard to say goodbye.