Up until October 1979 there were TWO. The 1st for the Jews, the 2nd for the Gentiles.
The Watchtower 2/15/1966 p. 126 Does Peter Now Use the Keys of the Kingdom? NO MORE KEYS NEEDED
The question arises, Did Peter continue to carry these keys of the Kingdom around with him to open to those whom he would and to close to others the opportunities for entering the Kingdom? Are there more keys besides the two? The answers are shown in the following facts. Up to this time Jehovah had divided up mankind into just two classes: the Jews, whom he dealt with as his special people, and the people of the nations, the Gentiles. So only two keys were needed.
After 1979 there were THREE. The 1st for the Jews, the 2nd for the Samaritans, the 3rd for the Gentiles.
The Watchtower 10/1/1979 p. 18 par. 12 The “Keys” of the Greatest Government Put to Use
Peter had been promised, not one key, but “the keys of the kingdom of the heavens.” This meant at least two keys. So, when was he given the second key, and in behalf of whom?
The Watchtower 5/15/2008 p. 30 Highlights From the Book of Acts
PETER USES “THE KEYS OF THE KINGDOM” (Acts 1:1–11:18) After receiving the holy spirit, the apostles give a bold witness. Peter uses the first of “the keys of the kingdom of the heavens” to open the door of knowledge and opportunity for Jews and proselytes who “embraced his word” to enter the Kingdom. (Matt. 16:19; Acts 2:5, 41) A wave of persecution scatters disciples, but this results in expansion of the preaching work. Upon hearing that Samaria has accepted the word of God, the apostles in Jerusalem dispatch Peter and John to them. By opening up the Kingdom opportunity to the Samaritans, Peter uses the second key. (Acts 8:14-17) Perhaps within a year of Jesus’ resurrection, an amazing transformation takes place in Saul of Tarsus. In 36 C.E., Peter uses the third key, and the free gift of the holy spirit is poured out upon uncircumcised people of the nations.—Acts 10:45.
Editor’s note: Special thanks to reddit user wemusthavethefaith for the references.