Musk first issued a call for testers back in September, asking for between 100 and 200 volunteers to step forward and join the internal testing program. It's not entirely clear if he's only offering to equip newly purchased Teslas with a full-fledged autonomous system at no cost, since Electrek says the company will retrofit participants' cars with the new hardware.

The Full Self-Driving Capability package costs $8,000 on top of the price of the car itself. In his message to employees, Musk apparently reiterated that all employees and customers who ordered the package will get a free upgrade to Tesla's Autopilot Hardware 3 computer. The CEO said Hardware 3 has "over 1000% more capability than HW2 (Hardware 2)."

Tesla is asking hundreds of hours of driving feedback in return for the free installation, telling employees that this is the last time he's making the offer. Musk is apparently hoping to collect enough data to be able to develop and roll out features leading to full autonomy by the end of 2019. The CEO is known to be a bit too optimistic when it comes to timelines, though, so Tesla owners may want to temper their expectations.

Here's part of Musk's message: