Exchange Tokens are a former steam inventory currency that was used to gain Arcade Tokens for the pet catchers in the arcade.
Exchange Tokens were replaced with Exchange Coupons in Version 1.31.6. The player was given 6 of these tokens in their Steam Inventory every three days, which would be converted into 3 arcade tokens upon completion of an online game. The player would have each the 3-day period during which they could earn the arcade tokens before the new exchange tokens would overwrite the previous ones. As a result, the cap for this item was 6.
Exchange Coupon grant period has been changed from every 3 days to be weekly: you now receive 15 coupons once per week whenever you log in, and can play up to 15 games to exchange them into Arcade Tokens.
Exchange Tokens (note: not Arcade Tokens) now get replaced when players receive new ones. This makes the effective maximum number of exchange tokens players can carry 6 as of the next time they are granted.