The annual session of the Indian National Congress in 1929 at Lahore was significant for the following reason:

(1) Proclamation of commitment to 'Purna Swaraj'.

This was when the Indian National Congress, under the leadership of Jawaharlal Nehru, passed a resolution declaring the goal of achieving complete independence from British colonial rule, known as "Purna Swaraj" or "complete self-rule." This marked a significant step in the Indian independence movement.

So, the correct answer is (1).