Genius Flag tiniest to Bronze/Silver/Gold Tiering

Your question is Genius Flag tiniest to Bronze/Silver/Gold Tiering. Take a moment with it on the right.

Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).

Problem

Design computing, storing and serving a near-real-time 'Genius' flag for 1B Booking.com customers (at least 2 completed bookings in last 2 years), re-evaluated after 2 years; later extend to Bronze/Silver/Gold tiers with upgrades and downgrades.

Asked in the system design stage. Reported follow-up: move from a boolean flag to a tier-based system.

Address:

Clarifying questions and scale estimates.
Event ingestion, eligibility computation, storage, and serving.
Near-real-time updates and two-year expiry handling.
A backward-compatible design for tier upgrades and downgrades.
Consistency, replay, privacy, monitoring, and failure recovery.

No fixed QPS, latency, or freshness target is provided. State the assumptions you need and explain how the design changes if those targets are stricter.

Your question is Genius Flag tiniest to Bronze/Silver/Gold Tiering. Take a moment with it on the right.

Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).

Asked in the system design stage. Reported follow-up: move from a boolean flag to a tier-based system.

Address:

Clarifying questions and scale estimates.
Event ingestion, eligibility computation, storage, and serving.
Near-real-time updates and two-year expiry handling.
A backward-compatible design for tier upgrades and downgrades.
Consistency, replay, privacy, monitoring, and failure recovery.

No fixed QPS, latency, or freshness target is provided. State the assumptions you need and explain how the design changes if those targets are stricter.