Apostra

Pioneer in agentic advertising infrastructure, providing the protocol layer and platform for AI agent-led media buying across omnichannel inventory

Apostra (formerly Scope3) is an agentic advertising company that enables advertisers and their AI agents to access media inventory directly across display, connected TV (CTV), audio, and out-of-home channels. The company rebranded from Scope3 in September 2026, marking a strategic pivot from its origins as a carbon emissions measurement and sustainability platform for the advertising industry toward becoming a foundational infrastructure layer for AI-driven ad buying. Apostra is built on the Ad Context Protocol (AdCP), an open standard that Scope3 helped create to enable AI agents to discover, evaluate, and transact on media programmatically. At its core, Apostra positions itself as the connective tissue between AI buying agents and media owners, removing traditional intermediaries and enabling a new paradigm of autonomous, agent-led media procurement. The platform gives AI agents the contextual signals and transactional access they need to make real-time buying decisions across multiple media formats, reflecting a broader industry shift toward agentic workflows in programmatic advertising. Founded by Brian O'Kelley — a veteran AdTech entrepreneur previously known for co-founding AppNexus — Apostra carries significant credibility in the programmatic ecosystem. Its transition from sustainability measurement to agentic ad infrastructure represents one of the more notable strategic pivots in recent AdTech history, and positions the company at the intersection of two major industry trends: AI automation and the ongoing evolution of programmatic media buying.