On the 28th of February 2026, Microsoft quietly switched off the DSP it had bought from AT&T four years earlier for around a billion dollars. The platform had previously been Xandr, and before that AppNexus — for more than a decade one of the most respected names in programmatic, the open web’s most credible non-Google challenger, the centre of gravity of the AT&T adtech ambition that valued it at $1.6 billion in 2018. By 2026 it was gone. Microsoft kept the supply side (Monetize) and the curation layer (Curate). The buy side it simply stopped supporting. When I entered Adtech in the late noughies, AppNexus was the poster child of innovation, it was everything which was great about adtech - category creating even - so on a personal level its demise left a gap.
Two months later, on the 21st of April, Index Exc…
