AppNexus
AppNexus provided publishers, advertisers, and agencies with an open, independent programmatic technology stack for real-time bidding, ad serving, and data-driven audience targeting — free from the conflicts of interest inherent in walled-garden platforms.
Last updated Jun 13, 2026 by ATDb automated enrichment
- Industry
- Programmatic Advertising & Ad Exchange Technology
- Business Model
- Marketplace
- Target Market
- Enterprise
- Employee Count
- 1001-5000
- Funding
- $292M
- Revenue Range
- $300M-$500M
- Stock Symbol
- N/A
- Parent Company
- Microsoft (via Xandr acquisition)
- API Available
- Yes
AppNexus was one of the largest independent programmatic advertising platforms globally before its acquisition, competing directly with Google's DoubleClick and serving as a preferred alternative for publishers and buyers seeking an open, non-walled-garden ecosystem.
AppNexus was one of the most influential independent programmatic advertising technology companies in the history of digital advertising. Founded in 2007 by Brian O'Kelley and others, the New York-based company built a comprehensive, open programmatic infrastructure that enabled publishers, advertisers, agencies, and ad networks to buy and sell digital advertising inventory in real time. Its platform encompassed a full-stack suite of demand-side, supply-side, and data management capabilities, making it a central node in the global programmatic ecosystem and a formidable rival to Google's DoubleClick. At its peak, AppNexus processed billions of ad impressions daily and was widely regarded as the largest independent ad tech platform in the world. The company attracted major agency holding groups, independent trading desks, and premium publishers as clients, and it positioned itself as an open, neutral alternative to walled garden platforms. It raised over $300 million in venture funding and was frequently cited as a likely IPO candidate before AT&T announced AppNexus acquisition on June 25, 2018 (closed August 15, 2018) for ~$1.6 billion, and publicly launched the Xandr brand at the AT&T Relevance Conference on September 25, 2018. AT&T sold Xandr (including AppNexus) to Microsoft in June 2022, ending AT&T's brief ad-tech bet's ambitions to build a data-driven advertising business. Following the acquisition, AppNexus was rebranded as Xandr in September 2018, named after Alexander Graham Bell, as AT&T sought to consolidate its advertising assets including Turner Broadcasting's ad sales under a unified brand. However, AT&T's ad tech ambitions proved short-lived; Xandr was sold to Microsoft in June 2022 for approximately $1 billion. Microsoft subsequently integrated Xandr's technology and capabilities into Microsoft Advertising, effectively dissolving the Xandr brand by 2023. AppNexus's legacy lives on in the programmatic infrastructure and open-exchange principles it helped establish across the industry.
AppNexus Marketplace
A real-time bidding exchange connecting buyers and sellers of digital advertising inventory at scale.
AppNexus Publisher Suite
A full-stack ad serving and yield management platform for publishers to monetize their digital inventory.
AppNexus Buyer Platform
A demand-side platform (DSP) enabling advertisers and agencies to purchase programmatic media across display, video, and native formats.
AppNexus Programmable Bidder
A customizable bidding engine allowing sophisticated buyers to implement proprietary bidding algorithms and optimization logic.
AppNexus Data Marketplace
An integrated data marketplace enabling audience targeting using first- and third-party data segments.
- 2007Founded
- 2018Rebranded to Xandr
- 2021Acquired by Microsoft Monetize
- 2021Acquired by Microsoft
- 2023Rebranded to Microsoft Advertising