U.S. shoppers spent a record $26.4 billion across all retail sites during Amazon’s four-day Prime Day event, and for the first time, the people most likely to complete a purchase were those who arrived from AI chatbots.

It’s the latest twist in a high-stakes bet by Amazon. The AI assistants now sending retailers their best-converting customers are the same ones Amazon has worked to keep away from its own store, hoping to keep shoppers coming directly to Amazon.com and using its own on-site AI assistant instead.

Adobe reported over that weekend that visitors who clicked through to shopping sites from AI assistants were 40% more likely to make a purchase during the four-day event than those showing up through search, email or social media.

AI still accounts for a small fraction of total shopping traffic, but a trend is starting to emerge. In the past, shoppers sent by AI were the least likely to buy, according to Adobe’s data. The change suggests that ChatGPT, Claude, Gemini and others are becoming more effective at giving shoppers the information they need to buy with confidence.

Those figures span all of U.S. retail — “Prime Day” has become much more than a day, and much bigger than Amazon alone. The distinction matters, because Amazon has taken a different path than many of its rivals. While Walmart, Target and others have opened their catalogs to outside AI assistants, Amazon has kept them out.

Agentic AI drives less than 1% of traffic across every major online store, but Amazon’s share is the lowest of the group, at about 0.4%, according to J.P. Morgan data.

That’s by design: Amazon sued Perplexity, for example, over its browser that shopped on customers’ behalf, and won a preliminary injunction barring the tool from the logged-in parts of its site, arguing that unauthorized shopping agents degrade a trusted experience. Perplexity is appealing.

Amazon has separately blocked ChatGPT’s crawlers from reading its listings — even as it has begun buying ads inside ChatGPT to bring shoppers back, a move first spotted by Marketplace Pulse founder Juozas Kaziukėnas and reported by Business Insider and Modern Retail.

On Amazon’s most recent earnings call, in April, CEO Andy Jassy said the company was in talks with the AI companies to come up with a better experience between Amazon and third-party agents to “find something that works for customers and all the companies.”

In the meantime, Amazon is focusing on its own AI assistant.

The tool — launched as Rufus and folded in May into a service called Alexa for Shopping — has drawn more than 250 million users, with monthly users up more than 115% over the past year, the company said. Customers who use it while shopping are more than 60% more likely to buy, and Amazon Web Services has said the tool drove nearly $12 billion in incremental sales last year.

Jassy said on the earnings call that third-party agents weren’t good enough yet — that they lacked a shopper’s history and often couldn’t get prices right — and that people would gravitate to whichever assistant knew them best. That’s the opening Amazon is going after with its own AI chatbot and related tools on Amazon.com.

“We are aiming to have it be the best shopping assistant anywhere,” Jassy said.

The strategy reflects one of the ways Amazon is increasingly making money. Advertising is now among its most profitable businesses. J.P. Morgan expects it to bring in about $83 billion in revenue this year and, because the margins are high, to account for roughly a third of the company’s operating income.

That advertising revenue depends on Amazon getting shoppers to browse its own site rather than handing the decision to an outside chatbot it doesn’t control.

The big question long-term is whether Amazon can maintain its own role as a primary destination for shoppers and avoid becoming just another selection on a chatbot’s shelf.