In late September, OpenAI first announced the Instant Checkout feature that will soon allow shoppers to buy items through Walmart, and said it would initially support purchases from Etsy sellers. OpenAI said at the time that more than one million Shopify merchants, including Skims and Glossier, would be coming soon.

Walmart Inc. was among the top performers on the Dow Jones Industrial Average on Tuesday and on pace to reach a new record high, after the big-box chain announced a partnership that will soon allow cu...