Generally no change for break-in. First change is typically at 20k miles, but there is nothing in the FSM about service intervals. Some manufacturers are filling with high quality synthetics and calling it good for the life of the vehicle. That's not to say you might be able to extend the service life well beyond 250,000 miles by changing it, just that the factories have determined they will get acceptable service life with the original lubricant.
Given the triple cone synchros for first and second, I'd say they expect this gearbox to last a very long time without issues.
FWIW, it holds 2.5 liters of 75w-90 API GL-4 or GL-5 gear lube. I expect I'll be putting Red Line MTL in it when the 20,000 mile mark rolls around. MTL works great in transaxles, it was designed for them.