GDANSK, Sept 14 (Reuters) - Poland's biggest video game developer CD Projekt will release an update to its flagship game Cyberpunk 2077 on Sept. 21, a company representative said on Thursday during a livestream on YouTube.

The update will launch just a few days before the premiere of Phantom Liberty, a highly-anticipated expansion of Cyberpunk 2077, set for Sept. 26.

The update - known as Cyberpunk 2077 2.0 - will be free and its features will include combat AI improvements, vehicle combat and car chases as well as improvements to User Interface and User Experience, and changes to police action in the game.

Cyberpunk 2077 2.0 will be available on PC, Xbox Series X|S and PlayStation 5.

In September last year, CD Projekt said it had sold 20 million copies of the game.

(Reporting by Adrianna Ebert; Editing by Susan Fenton and Jane Merriman)