Ultimate tic-tac-toe

Compared to traditional tic-tac-toe, strategy in this game is conceptually more difficult and has proven more challenging for computers.

Although elementary evaluation functions can be made for ultimate tic-tac-toe by taking into account the number of small board victories, these largely overlook positional advantage that is much harder to quantify.

Therefore, computer implementations using these algorithms tend to outperform minimax solutions and can consistently beat human opponents.

Not many online UTT platforms exist due to the games decreased popularity and limited player counts.

Few players have formulated theory behind UTT, such as openings and winning strategies however current communities exist for this objective.

[7] If playing with this rule set is still preferred, the forced-win problem can be practically solved by generating the first 4 moves at random.

An incomplete board of Ultimate Tic-Tac-Toe.
Incomplete ultimate tic-tac-toe game (the large 'X's and 'O's represent small boards that are won by that player). The previous move was O playing in the center square of the bottom-right board, forcing X to play their next move in smaller board located in the center of the larger board (highlighted in blue).
Since X played in the top-right corner of the small board, O is forced to play their next move in the top-right small board of the larger board (highlighted in red).