One welcome bonus per card product, ever — enforced by a pre-submission pop-up you can safely test.
What it is
Amex grants each welcome bonus once per person per card product, for life. The enforcement mechanism is unusually humane: if you're ineligible, a pop-up appears before you submit, and closing the application at that point costs nothing — no hard pull, no record. This makes checking free: fill out the application, watch for the pop-up, and withdraw if it appears.
Current reports
Pop-up frequency has been rising for people who held the Gold card between 2019 and 2021, consistent with Amex tightening its lookback. No-lifetime-language offers — versions of the application that omit the restriction — continue to circulate via some referral links, and remain the main path for repeat bonuses.