The news: Amazon will double the length of its flagship Prime Day sale this year to four days, per an internal memo to third-party sellers seen by Modern Retail. That will make it the longest Prime Day event in the retailer’s history.

Why the move makes sense: There are several benefits to a longer Prime Day event.

• More ad revenues. Advertisers spend big on the lead-up to and during the sales event, making it an important contributor to the retailer’s fast-growing ad business.
• More sales. Extending the length of the sale gives shoppers more opportunities to take advantage of deals—which could be especially alluring if tariffs and other economic uncertainty dent consumer buying power and confidence.
• The four-day event could also help the retailer counter the likes of Walmart, Target, and TikTok Shop, which have been holding competing sales in the lead-up to Prime Day in an effort to steal shoppers away.

Our take: Amazon is steadily increasing the length of its sales events—which could be in deference to shoppers’ growing cost-consciousness, but is also a relatively easy way (in the short term) to boost YoY growth.

• The retailer launched its Black Friday sale a week early last year, reflecting the shift from the Cyber Five to the Cyber Dozen.
• It also extended its Big Spring Sale by an extra day.

While Prime Day is far from the month-long extravaganza that is Singles Day, it could be headed in that direction. That said, as Alibaba and JD.com have discovered, there are limits to how far that strategy can go before it delivers diminishing returns.