Tesla CEO Elon Musk gave owners of its Roadster a bit of a present on Christmas Day: The Roadster will indeed get nearly 400 miles range potential he said on Twitter.

The news was expected from prior reports and hints, and last Friday Musk had tweeted news was coming.

Specifics in the 140-character communication format naturally were not forthcoming, nor did Musk offer a supplemental blog post or other info. Instead, he said more details would be released today.

Via Twitter.

Via Twitter.

A second tweet at the same time on Christmas day said owners of the Model S – presently rated for 208-265 miles – will not be getting a similar range-boosting offer.

“Should mention that a battery pack upgrade is not coming soon for the Model S, but it obviously *will* happen long-term,” tweeted Musk.

The 244-mile rated range Roadster is presently not compatible with Supercharger charging stations that were designed around the Model S and for subsequent models to come. Musk’s tweet did not say whether this would be made possible.

Further, no indicators were given of potential costs to the upgrading Roadster owner or other caveats to the “almost 400 mile” range increase but we’ll have more later when Tesla says more.

UPDATE: Dec. 26 – More details now posted.