The FAQ suggests that once you cross the install threshold, you keep paying. The thresholds are "lifetime"
>The Unity Runtime Fee will apply to this game, as it surpasses the $1M revenue and 1M lifetime install thresholds for Unity Pro. Let’s look at the game’s installs from the last month:
Prior month installs (Standard fee countries) - 200K
Prior month installs (Emerging market fee countries) - 100K
The fee for install activity is $23.5K USD, calculated as follows:
(100K x $0.15 (first tier for standard fee countries)) + (100K x $0.075 (second tier for standard fee countries)) + (100K x $0.01 (fee for emerging market countries)) = $23.5K USD
>The Unity Runtime Fee will apply to this game, as it surpasses the $1M revenue and 1M lifetime install thresholds for Unity Pro. Let’s look at the game’s installs from the last month: Prior month installs (Standard fee countries) - 200K Prior month installs (Emerging market fee countries) - 100K
The fee for install activity is $23.5K USD, calculated as follows: (100K x $0.15 (first tier for standard fee countries)) + (100K x $0.075 (second tier for standard fee countries)) + (100K x $0.01 (fee for emerging market countries)) = $23.5K USD