Announced as part of the 2017 A4, it's thin on details though:
Quote:
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This optional feature works in conjunction with adaptive cruise control, automatically adjusting the set speed for terrain, curves in the road and speed limits. Audi notes that this system can increase fuel economy by 10 percent.
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From:
2017 Audi A4 Preview - CNET
I'm assuming it's saving fuel by avoiding abrupt speed changes, and possibly driving with load on elevation changes.