The line between personal assistant and advertising vehicle has always been a thin one, but Amazon has now erased it entirely — or at least reduced it to the width of a text message.

The company said today that it has begun letting a small group of customers in the United States shop by texting a contact called "Alexa Shopping," as if it were a particularly well-organized friend who happens to have access to the world's largest retail catalog. The service searches, compares, suggests and buys, all through the same interface people use to argue with relatives and share photographs of their lunch.

For advertisers, the opportunity arrives at what Amazon is calling the "discovery stage" — the moment when the digital assistant texts back a handful of options and a customer decides which one to buy. Sponsored Products can now appear among those suggestions, which puts brands inside one of the more intimate spaces on a mobile phone, competing for attention with perhaps three or four alternatives rather than the endless scroll of a search results page.

Amazon is not yet charging for these placements, which gives the company a low-cost laboratory for determining how much advertising people will tolerate in what feels like a private conversation. (The answer, historically, has been "more than they say they will, but less than advertisers hope.")

The company said more than 400 million customers have used Alexa for Shopping in the past year, and that use of its so-called agentic features — the ones where the software acts on your behalf — has grown eightfold since January.

"As agentic commerce meets advertising, the definition of an impression is critical," said Jonathan D'Sousa-Rauto, an independent ad technology consultant, raising the sort of measurement question that tends to generate many meetings and few answers.

Amazon has, for now, kept the advertising to the moment before purchase rather than letting a sponsored product slip into an order the agent completes automatically. That restraint may not survive contact with a quarterly earnings call, but for the moment, customers who ask the agent to reorder dog food can rest assured the bag on the doorstep will be the one they wanted.

Or at least the one the algorithm thinks they wanted, which is increasingly the same thing.

Original story published in Digiday: "Amazon's shopping agent now takes orders by text, with Sponsored Product ads in the replies"