Third-party sellers accounted for 60% of paid units sold on Amazon in Q1 2026, down from 61% in Q4 2025 and 62% the quarter before that. It’s the first time the metric has fallen for two consecutive quarters since Amazon began breaking it out in its quarterly reports in 2004.For more than a decade, the marketplace share has only moved one way. Between 2013 and 2016, it gained a percentage point every single quarter for eleven straight quarters. The share peaked at an all-time high of 62% in Q4 2024 and held within a 61-62% range for five consecutive quarters before this back-to-back decline.Groceries appear to be the largest factor. Paid unit growth hit 15% in Q1 – the highest since the tail end of COVID lockdowns – and 1P unit growth outpaced 3P for the quarter. Amazon disclosed on its Q1 earnings call that perishable sales grew 40x year over year and now make up nine of the ten most-ordered same-day items where the service is available. Whole Foods operates over 550 stores, and Amazon’s broader grocery business reached $150 billion in gross sales in 2025 – roughly 18% of the company’s estimated $830 billion total GMV. Grocery – and perishables in particular – is largely fulfilled through Amazon’s own grocery network of Whole Foods, Amazon Fresh, and same-day hubs rather than the third-party marketplace, so its expansion shows up almost entirely in Amazon’s own unit count.The more interesting wrinkle sits one level up. Even as first-party retail reclaimed unit-mix share, online stores fell to 35.4% of net sales – an all-time low since Amazon began breaking out the segment in 2016, down from 36.9% a year earlier. Third-party seller services edged down modestly to 22.9% from 23.5% in Q1 2025. Both segments grew in absolute terms – online stores up 9% on a constant-currency basis and third-party seller services up 12% – but were outpaced as a share of net sales by AWS at 28% growth and advertising at 22%. AWS now represents 20.7% of net sales, its highest share ever, with growth accelerating to its fastest pace in 15 quarters on a $150 billion annualized run rate, driven by surging customer demand for AI compute.Two consecutive 100-basis-point declines do not bury the long-running 3P-share thesis – sellers still account for 60% of units and the estimated 69% of GMV – but they do confirm that the unrelenting climb has plateaued. Grocery’s growing share of Amazon’s unit volume is a dynamic that did not exist at scale during the marketplace’s expansion years. The marketplace continues to grow, but Amazon’s growth story is increasingly being told outside it – in AWS, in advertising, and in the agentic commerce layer now being built on top of both.