Marketers Pivot Spending for AI-Driven Discovery, But Measurement Systems Fall Behind

IAB's "2026 Outlook Study: September Update" found that while advertisers are rapidly shifting focus to optimizing for AI-generated answers and AI LLM models, their measurement infrastructure is lagging significantly behind. Forty-five percent of ad buyers cite comparing AI-driven and traditional customer journeys as a major measurement challenge, with additional pain points including inconsistent data on brand visibility in AI tools (35%) and unreliable AI referral data (30%). In response, 86% of marketers are changing or plan to change their measurement approaches within 12 months, with most combining multiple signals—brand visibility in AI tools, branded search proxies, third-party analysis tools, incrementality tests, and modeled measurement—layered atop traditional website traffic metrics rather than replacing them entirely. The survey of 211 U.S. brand and agency decision-makers also revealed that AI is accelerating spending shifts, particularly into retail media, which IAB now forecasts will grow 13.6% this year, while creating new complications around distinguishing human traffic from legitimate agents and bots.