Age of Empires 3 Offline Play: Product Key Required for Steam, Not for Disc

Depends on your version:

• Original Retail Disc (2005): Install from disc → play offline. Disc check required at launch. No key entry after install. Key was used once during initial install.
• Steam Version: Requires Steam account + online activation once. After first launch (online), you can play offline via Steam Offline Mode. No separate "product key" — the license is tied to your Steam account.
• Microsoft Store / Game Pass PC: Requires Microsoft account + online check every 30 days.
• GOG Version (Definitive Edition): DRM-free. Install offline, play offline forever. No key, no client required after download.

Summary