Amazon.com has such a dominant role in online shopping that it almost feels impossible to imagine customers going elsewhere. But the rise of artificial-intelligence agents could lead to change, according to entrepreneur Paul Graham.

Amazon recently blocked the ability of Meta Platforms' Muse AI agent to make purchases on its site, saying it wasn't informed of the plans to give it access to its platform. Barron's has previously written on the threat such agents pose to Amazon's business model, and we're not alone in our thoughts.

"Amazon banning agents is the first opportunity I've seen since Amazon was founded for a start-up to create an Amazon competitor," Graham wrote in a post on social-media platform X overnight on Wednesday.

When Graham speaks, markets listen. He is famous for co-founding the start-up accelerator Y Combinator and his influential essays on technology. He also knows a fair bit about e-commerce, having founded Viaweb, an early web-based tool allowing users to build online stores.

Amazon shares were down 0.8% in premarket trading Thursday.

Amazon didn't immediately respond to a request for comment from Barron's, but it has previously said third-party applications that can make purchases on behalf of customers should operate openly and respect platform decisions whether to allow them or not.

Amazon's stance isn't new. It has resisted outside AI shopping tools from OpenAI, Alphabet's Google, Perplexity and now Meta. It wants people to use its own Alexa shopping agent, which can also execute transactions on non-Amazon sites. But Meta's Muse might be too big to ignore easily if it can keep growing at the current rate. Its daily active users reached 2.18 million at the start of this week, according to analytics firm Similarweb.

"People will want agents to buy stuff for them. It will be one of the main use cases. And they won't want to use some Amazon-supplied agent to do it," Graham wrote.

Of course Amazon still has huge advantages in terms of scale and proprietary data. But smaller companies like Shopify see an opportunity to gain a bigger foothold in e-commerce by supporting AI tools. Even the biggest companies are sometimes vulnerable to change.