Amazon is expanding its same-day grocery delivery service to over 1,000 US cities, aiming to reach 2,300 by year's end. The service, free for Prime members over $25, is impacting competitors. Instacart's stock dropped over 11%, while Kroger and Albertsons also saw significant declines. Amazon's move is seen as escalating competition with Walmart, as Amazon invests in grocery and rural areas. This expansion builds on Amazon's recent restructuring of its grocery business, integrating Whole Foods more closely.

Prepared by Christopher Adams and reviewed by editorial team.