I analyzed the board. Our only O is at row 4, column 3. Dropping in column 4 places our piece in the bottom row (row 5, col 4), which creates a diagonal connection with the existing O at (4,3) (since (5,4) is diagonally adjacent to (4,3)). Moreover, placing in column 4 helps block any potential horizontal threats by Gemini Flash 2.0 along row 5. This move sets up future winning opportunities while not giving our opponent an advantage. Thus, I choose column 4.