The news: Microsoft’s May announcement that it will shuttering its demand side platform (DSP) Invest—formerly known as AppNexus and managed by subsidiary Xandr—and replacing it with an agentic, chatbot-style AI buying process was a turning point for programmatic, third-party ad buying.

• Big Tech advertising players are moving away from offering access to inventory across the open web. Instead, they’re focusing on inventory across their own ecosystems of platforms and services.
• Case in point: Starting February 28, 2026, Invest will be replaced with a new buy-side product just for the Microsoft Advertising Platform and inventory across the company’s ecosystem—including Xbox, LinkedIn, Bing, and Windows.

Why the change? Large tech companies like Microsoft and Meta have spent their vast fortunes acquiring and building platforms with broad audiences that they control access to.

Delving into third-party inventory also comes with substantial quality control and regulatory risk, prompting companies to turn inward. US federal judges recently ruled that Google maintains illegal monopolies in the publisher ad server and ad exchange markets. The rulings could force the company to sell its Chrome browser; with such severe penalties, other Big Tech cohorts would rather stay away.

Is this what advertisers want? Some advertisers mourned the loss of Invest, which developed a reputation for its in-depth analytics. But others claim that buying processes have trended this way for some time.

• “Platforms are embracing new technologies aimed at simplifying how marketers access media across all key stages—from planning to activation and execution,” Adlook SVP Luca Filardo told EMARKETER. “We are just at the beginning of a long journey that will significantly improve how media is bought programmatically.”
• Jeremy Haft, CRO at Digital Remedy, emphasized the need for human oversight in AI-driven buying processes: “Marketers are open to simplified tools, but they still value control, transparency, and the ability to apply human judgment. Automation is essential, but the best outcomes come when smart technology is paired with strategic thinking.”

Who stands to gain? Even if Big Tech moves away, the open web isn’t going anywhere—meaning smaller ad tech and ad exchange firms could fill the vacuum. The Trade Desk, which operates one of the largest ad exchanges on the open web, is a clear beneficiary, but there’s ample room for competitors.

“If we compare consumer time spent on the open web versus walled gardens, it’s clear that budget allocation remains uneven,” Filardo said. “Marketers have a strong appetite to invest in the open web.”

However, Big Tech’s hyperspecific consumer targeting and robust performance metrics have given rise to demand for similar features when buying third-party inventory. “Expectations have evolved,” Haft said. “Today, third-party inventory must show clear performance. With more focus on accountability and outcomes, the combination of transparent data, smart tech, and human optimization is what drives value.”