The policy is in Tesla's blog post. Read it. And yeah, 400kWh isn't much if you use superchargers for long trips, but if you just need them for accidental emergencies I guess it saves you from having to pay. I expect they'll be tweaking the limit over time as they see what people do and how the network holds up.
Here is the announcement from Tesla:
AN UPDATE TO OUR SUPERCHARGING PROGRAM
The Tesla Team November 7, 2016
Four years ago, Tesla introduced the Supercharger Network – the world’s fastest charging solution – to enable convenient long distance travel. Today, more than 4,600 Superchargers allow over 160,000 Tesla owners to drive across the continental U.S., from the Arctic Circle to the south of Spain, and across all of the population centers in China and Japan, among many other places. Supercharging has even helped owners drive their Teslas around the world.
We’ve designed our network so that all customers have access to a seamless and convenient charging experience when they’re away from home, as our intention has always been for Supercharging to enable long distance travel. That’s why today we’re announcing a change to the economics of Supercharging – one that allows us to reinvest in the network, accelerate its growth and bring all owners, current and future, the best Supercharging experience.
Ensuring Use for Long-Distance Travel For Teslas ordered after January 1, 2017, 400 kWh of free Supercharging credits (roughly 1,000 miles) will be included annually so that all owners can continue to enjoy free Supercharging during travel. Beyond that, there will be a small fee to Supercharge which will be charged incrementally and cost less than the price of filling up a comparable gas car. All cars will continue to come standard with the onboard hardware required for Supercharging.
We will release the details of the program later this year, and while prices may fluctuate over time and vary regionally based on the cost of electricity, our Supercharger Network will never be a profit center.
These changes will not impact current owners or any new Teslas ordered before January 1, 2017, as long as delivery is taken before April 1, 2017.
The Road Ahead Just as you would charge your cell phone, we believe the best way to charge your car is either at home or at work, during the hours you’re not using it. For travelers, the Supercharger Network has become a powerful, unique benefit of Tesla ownership. As we approach the launch of Model 3, this update will enable us to greatly expand our Supercharger Network, providing customers with the best possible user experience and bringing sustainable transport to even more people.
