pubX raises £3.8m led by Chicago Ventures after acquiring Compliant
This article covers pubX, a London martech startup, which has raised £3.8m in a series A funding round led by Chicago Ventures and announced the acquisition of Compliant, a media quality and governance business. The development supports pubX’s US expansion and the build-out of demand-side and agent-to-agent advertising capabilities, integrating Compliant’s quality signals to affect brands, agencies and publishers in programmatic markets.
pubX, a London martech startup, has raised £3.8m in a series A funding round led by Chicago Ventures and announced the acquisition of Compliant, a media quality and governance business. The cash injection and deal — terms of the acquisition were not disclosed — fund pubX’s US expansion, the build‑out of its demand‑side capabilities and further development of its buyer and seller agents built on the open Ad Context Protocol.
Why it matters
The funding and acquisition bring together publisher‑side inventory expertise and demand‑side quality signals under one roof. pubX positions itself as infrastructure for agent‑to‑agent advertising — software agents that plan, buy, sell and optimise media directly between buyers and sellers. If the approach works in practice, it promises to shift spend toward measured, auditable transactions and to change how discoverability and quality are recognised in programmatic markets.
The move also highlights continued investor interest in infrastructure plays within martech, where trust and governance are increasingly central to brands and agencies.
Inside the product
pubX builds buyer agents and seller agents that transact directly with each other from brief to reporting, using the Ad Context Protocol (AdCP) to standardise signals and decision logic across channels. The company emphasises governance built into every transaction: agents apply checks, record reasoned and auditable decisions, and operate within client‑defined briefs and commercial rules so humans remain in control.
Compliant, founded by former Unilever and P&G executives, brings the Data Integrity and CTV Quality Indexes that measure media quality and audience validity. pubX says those signals will be integrated into agent decisioning so quality metrics are considered before a buy is executed.
The funding will support work on the demand side — serving brands and agencies — integration of Compliant’s signals across the platform, and expansion in the United States.
Who are the investors?
The series A was led by Chicago Ventures. The announcement does not list other participating investors.
In the announcement, Stuart Larkins, Co‑founder & General Partner at Chicago Ventures, said:
Every part of the advertising industry is asking how agents will improve buying and selling, and most answers so far are an agentic layer built on existing infrastructure. Co‑founders Andrew Mole and Alex Rosen, pubX's CTO, have built advertising infrastructure before, and this time they built it for agents from the start, on both sides of the transaction, with a publisher base that already trusts them and a design that keeps the client in control. That is a rare starting position, and the Compliant acquisition makes it stronger.
The investor rationale emphasises pubX’s infrastructure‑first approach and the strategic value of combining publisher relationships with demand‑side quality signals. Chicago Ventures’ lead indicates US VC interest in cross‑border martech infrastructure focused on governance and transparent measurement.
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Founder perspective
In the announcement, Andrew Mole, CEO and co‑founder of pubX, said:
Programmatic took this industry from fax machines and spreadsheets into more automated and real‑time platforms in two short decades, and everything we've done since builds on that premise. Agents let us finish what was started. You tell them how you buy, you sign off where it matters, and every page of the brief gets read every single time. For the first time, the infrastructure has caught up with what brands want to achieve with their advertising and how publishers want to sell.
In the announcement, Jamie Barnard, CEO of Compliant, said:
For years, brands have searched for high‑quality, high‑performing inventory with real, relevant and engaged audiences. Compliant built the Data Integrity and CTV Quality Indexes so that they could do that with certainty rather than speculation. Inside pubX, those media quality and governance signals sit in the decision itself, so an agent weighs them before it buys. This is what gives each CMO the confidence to trust pubX's agents.
Both founders frame the integration as solving a longstanding gap between brand demands for transparency and publishers’ need to be discoverable to buyers.
The bigger picture
pubX’s approach surfaces three industry trends: the move from opaque programmatic pipes to auditable decisioning; the commercial value of first‑party publisher data for discoverability; and demand from brands for integrated quality signals in buy decisions. Partners cited in the announcement — Paradium.AI (formerly The Arena Group) and USA TODAY Co. — are examples of publishers positioning first‑party audiences and brand‑safe environments to be visible to AI‑driven buyers.
pubX plans a live agent‑to‑agent buy at Advertising Week New York, running a campaign for Reckitt’s Mucinex from brief to live placement with publisher participation. The test will be an early practical demonstration of the model in front of agency and brand stakeholders.
This deal also reflects a pattern of US investors leading rounds for UK martech infrastructure companies, as larger advertising budgets and testing opportunities in the US become central to growth plans.
The pubX story will be watched by martech investors, publishers and brands in the UK and Europe as they assess whether agent‑based buying, combined with embedded governance, can deliver more transparent, higher‑quality media markets.
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