Your Buyer Tier is reviewed annually on January 1st.
Buyer Tier Maintenance Rules
To maintain your current Buyer Tier, you must meet the minimum annual spending requirement for that tier within the calendar year.
If you do not reach the required spending amount, your Buyer Tier will be downgraded by one level on January 1st.
Tip: You can check your progress toward maintaining or upgrading your Buyer Tier at any time in your profile.