Today was the first time I seen any detail about this, so here goes:
The new Code Geass project titiled Geass Gaiden: Boukoku no Akito (Akito of the Ruined Nation) is a side story that takes place in a.t.b. 2017 (during the time of the first “season”) on the European battlefront. A platoon of young soldiers sent from Zone (Area?) 11 are sent into a military operation with 5% chance of survival.
The project will be planned out by Code Geass creators Goro Taniguchi and Ichiro Okouchi, while the production will be directed by Sunrise alums Kazuki Akane (Escaflone: The Movie, Noein, Gundam: 0083, Birdy the Mighty DECODE) and written by Shigeru Morita (Blood +, Gundam SEED, Toward the Terra). Takahiro Kimura and Akira Yasuda will return as Animation Character Designer and Mechanical Designer, respectively.
No idea of format (TV, OVA) at this time. Stay Tuned