Got this in the email today:
Ends February 11, 2021
We know you love earning extra rewards on your Amazon.com and Whole Foods Market purchases with your Amazon Rewards Visa Card.
Now, we're giving you the opportunity to earn 4% Back everywhere else you use your card until February 11, 2021. So instead of earning 2% Back at restaurants, gas stations and drugstores, and 1% Back on everyday purchases, you'll earn a total of 4% Back in all of these categories.
Purchases must post to your account by February 11, 2021. This offer doesn't include purchases at Amazon.com or Whole Foods Market.
Activate 4% now
Activate by September 22, 2020
From the fine print there doesn't seem to be a limit:
During the promotional period, earn a total of 4% Back on the purchases made with your Amazon Rewards Visa Signature card that normally earn 2% and 1% Back. That's an extra 3% Back in addition to the 1% Back you earn on the purchases in the 1% Back category and an extra 2% Back in addition to the 2% Back you earn on purchases in the 2% Back category. To be eligible for this offer, you must log on to the website referenced in this offer and activate by 09/22/20, 11:59 PM ET. All purchases eligible to earn the extra % Back during the promotional period 08/11/2020 to 02/11/2021, including those that occurred during the promotional period prior to meeting the offer requirements, will automatically earn the extra % Back and be reflected on a future billing statement. The extra points earned for this promotion during the applicable monthly billing cycle are generally available to be used at the beginning of the next billing cycle; bonus points earned on purchases made near the end of a billing cycle may take up to one additional billing cycle to become available. To qualify for this promotional offer, your account must be open and not in default at the time of fulfillment. This promotional offer is non-transferable. For more information about your rewards program, see your Rewards Program Agreement.
The graphics in the email includes the regular Amazon card, so I'm not sure if the non-Prime version has this as well.