On a conference call today, Tesla just announced that it will offer an upgrade to a 90kWh battery on its Model S sedan for $3,000 extra. This represents a 5-kilowatt upgrade against the existing 85kWh model. This turns the car into a "90D" model instead of the existing 85D, offering 300 miles of highway range at 65 miles per hour. That represents a five percent improvement in range against the 85 — and perhaps more importantly, it cracks the 300 mark, which is something of a milestone (and perhaps a psychological barrier for some buyers).
CEO Elon Musk noted that existing Model S owners would also be able to upgrade to the 90-kilowatt pack, but he wouldn't recommend doing so unless they're near the end of their packs' battery lives because he expects range to continue to improve year-over-year — in other words, if you wait another year or two, you'll get an even better range.