I've had the Macy's store card for two years now, having been given the starting limit of $300 back in April 2017. In the two years since, my limit has made gradual increases to $15,000. When I went to pay my card this month, I was told I'd been automatically upgraded to the Amex card. My balance has never gone above $700 or so, so I get the feeling they're just trying to get me to use the card more. I'm still happy about this, but I also don't plan to use it any more than I did and will try to treat as if it were still just a store card.
I was upgraded just last week as well. Mind you I’ve had a Macys card since 94 and it’s my second oldest card. It only has a $1000 limit and still does. I rarely use it and won’t with that low limit but keep it open for age purposes. I won’t do a hard pull for an increase as I have enough credit with my other cards.
Congratulations on your upgrade!