Break-in period

The consensus on Prius Chat is that engine break-in strategies don't matter much to the Prius. Most modern automobiles are retired because of failure of multiple ancillary systems, not engine failure, so benefits of engine break-in are dubious. On top of that the Prius computer will not let you over-rev the motor anyway.

Several users have reported a burning smell in the first few hundred miles. It goes away and doesn't seem to be anything to worry about. At least one person attributed to the cosmoline residue burning off - a protection coating for the sea voyage.

Several users have noted improvements in fuel efficiency over the course of the first 10,000 miles.
After Break in Period = Better Gas Mileage? | PriusChat

If you're really fussy about break-in, check your manual, although they just seem to contain cut and paste recommendations from other cars. From page 151 of the 2010 Prius Owner's Manual:

And if it's too late to do that, just do an early first oil change and a transmission fluid drain/refill at 30k miles. Both are a good idea in a Prius.
Read more: http://priuschat.com/threads/engine-break-in-period.93752/