Magnite builds seller agent into SpringServe for AI-driven ad buying

Magnite integrated a seller agent directly into its SpringServe platform and completed its first agentic advertising test in December, positioning the independent supply-side platform at the center of an emerging automated buying framework that could reshape how premium streaming inventory reaches advertisers.

The company announced on January 6, 2026, that it embedded seller agent capabilities within SpringServe to support the Advertising Context Protocol, an open standard that enables artificial intelligence agents on both buy and sell sides to communicate campaign requirements, match inventory, and place campaigns without traditional request/response infrastructure. Scope3 served as the buyer agent in Magnite's initial December test, with additional pilots scheduled for early 2026.

"Magnite's role is to bring our publisher clients demand across any rails buyers choose to transact upon—whether that's programmatic, IO workflows, or emerging agent-driven channels," according to the company's announcement. The seller agent allows publisher partners to engage in AdCP tests, modernize one-to-one buying methods through automation, collaborate with emerging buyer agents, and participate in defining the agentic advertising category.

The implementation represents Magnite's response to industry momentum around AdCP that began on October 15, 2025, when six companies including Scope3, Yahoo, PubMatic, Swivel, Triton Digital, and Optable launched the protocol. Built on Anthropic's Model Context Protocol, AdCP establishes protocols for buyer and seller AI agents to interpret campaign goals, inventory, and audience signals using large language models rather than traditional programmatic mechanics.

The framework operates through a distinct workflow where buyer agents translate campaign briefs into structured intent, seller agents match that intent with appropriate audiences and inventory, and both sides agree before campaign placement occurs. According to Magnite, the vision promises simpler buying workflows, broader access to premium ad products, lower operational costs, and reduced tech tax, though the company acknowledges the framework remains extremely early with several critical components still being defined.

Early proofs of concept push campaigns into ad servers, but Magnite noted the industry ultimately needs scaled systems supporting hundreds of thousands of campaigns with sophisticated optimization. The company positioned seller agents as increasingly important in a world where both buyers and sellers use AI representation, emphasizing the sell side's role in enabling supply intelligence, curation, and scaled execution.

Major publishers testing Magnite's seller agent provided perspectives on how agent-driven workflows could reshape premium inventory transactions. Mike Evans, SVP and Head of US Sales at LG Ad Solutions, stated that "as a global CTV publisher, LG Ad Solutions is focused on technologies that help buyers better understand and activate against our premium inventory. Magnite's early work with seller agents marks an important step toward a more automated, intelligence-driven marketplace."

John Goulding, Global Chief Strategy Officer at MiQ, confirmed participation in early testing. "In December we set live one of the first AdCP buys working with Magnite's seller agent," Goulding stated. "We're hopeful this can bring even more supply into the programmatic sphere, and present new ways to deliver client outcomes. In 2026 we're excited to start scaling agentic ad buying through MiQ Sigma's trading agent."

Todd Overstreet, SVP of Ad Technology and Operations at Warner Bros. Discovery, emphasized how testing provided insight into agentic decisioning. "Testing Magnite's seller agent has given us a look into how agentic decisioning can elevate the precision and clarity with which our supply is understood and activated," Overstreet stated. "We see meaningful potential for these emerging workflows to strengthen publisher value, expand access to premium supply, and help shape a more open, intelligence-driven marketplace across linear and digital supply."

The seller agent deployment arrives as Magnite strengthened its position in connected television advertising, reporting 18% CTV growth in its third quarter 2025 results announced November 5. The company's SpringServe platform, which combines ad serving with supply-side platform capabilities, maintained its position serving 99% of US streaming supply according to Jounce Media's March 2025 benchmarking data.

SpringServe clients include Disney Advertising, LG Ad Solutions, Paramount, Roku, Samsung, and Warner Bros. Discovery. The platform introduced machine learning capabilities on October 24, 2025, to optimize ad pod construction for connected television publishers, reducing redundant bid requests while maintaining yield and competitive separation between brands.

Magnite's decision to embed the seller agent directly within SpringServe contrasts with alternative integration approaches. The company emphasized building within its existing infrastructure rather than creating standalone agent systems, allowing rapid learning and ensuring that whatever transactional rails buyers adopt, Magnite remains positioned to deliver demand to publishers.

The broader industry context shows divided responses to agentic advertising protocols. Industry veteran David Kohl warned on October 15, 2025, that AdCP represents premature focus on automation tools before addressing fundamental structural issues. Kohl argued that rushing to build agentic advertising infrastructure without clear goals risks repeating mistakes that created today's dysfunctional programmatic supply chain.

Ari Paparo questioned AdCP's media buying viability on November 3, 2025, while expressing support for creative automation specifications. Paparo raised concerns about whether agents can overcome fundamental business problems including pricing transparency resistance, scale economics, and data fragmentation that historically prevented programmatic direct success.

Augustine Fou and Christopher F. debated AdCP viability in December 2025, with both expressing skepticism about protocols enabling AI agents to buy advertising directly from publishers without intermediaries. Fou warned that AdCP relies on self-declaration that fraudsters will exploit, similar to how ads.txt was subverted from its first day. Christopher F. explained that major platforms lack business incentive to adopt protocols reducing vendor lock-in.

However, supporters argue standardization addresses critical industry needs. Ben Kahan, senior director of programmatic at Brainlabs, defended the effort, stating "the industry goes through eras, and now we seem to be entering an agentic era. But everything is siloed or fragmented. There hasn't yet been a push for standardization across any of it."

PubMatic launched AgenticOS on January 5, 2026, positioning the infrastructure as the first operating system built specifically for autonomous advertising execution across premium digital environments. The company, which co-founded AdCP alongside Yahoo, LG Ad Solutions, and Raptive, reported live campaigns running through its agentic infrastructure.

Swivel introduced agentic transaction capabilities on November 4, 2025, establishing direct connections between buyer and seller artificial intelligence agents that bypass traditional bidstream infrastructure. CEO Joseph Hirsch stated the company would activate the first revenue-generating agentic buy in November.

The competitive landscape includes major platforms building agentic capabilities into existing systems rather than adopting external protocols. LiveRamp donated the User Context Protocol to IAB Tech Lab on November 3, 2025, establishing an open standard for how AI agents exchange identity, contextual, and reinforcement signals across advertising systems. IAB Tech Lab introduced its Agentic RTB Framework version 1.0 for public comment on November 13, 2025, standardizing containerized agent deployment in real-time programmatic advertising.

Platform providers including Google, Amazon, and Meta are building agentic capabilities into their existing systems. Lindsay Rowntree, COO at ExchangeWire, noted during a podcast discussion that these major platforms have not signed up for recent agentic protocols, potentially creating more fragmentation through new walled gardens rather than solving existing coordination problems.

Magnite's measured approach reflects acknowledgment of both potential and uncertainty. The company emphasized that while far too early to predict outcomes, industry momentum and potential efficiency gains make agentic advertising "a space worth engaging in thoughtfully." Building the seller agent in SpringServe allows collaboration with innovators while ensuring delivery capacity regardless of which transactional rails buyers ultimately adopt.

The technical implementation enables sellers to expose first-party data including automatic content recognition data, transaction history for retail media networks, show-level data, content, context, and both traditional and custom inventory configurations. According to industry documentation, seller agents operate exclusively inside seller ad platforms, eliminating traditional data leakage concerns and preventing sharing sensitive information to demand-side platforms.

Magnite's announcement positioned the company to help shape what it describes as "an open, interoperable future" while maintaining its core function of delivering demand to publishers across any transaction method. The first December test established proof of concept, with planned early 2026 pilots designed to validate whether agent-driven workflows can deliver on their efficiency promises at scale.

The company acknowledged that several critical pipes remain undefined and tests are just coming online, but argued the promise justifies thoughtful exploration. According to Magnite, AI lowers barriers for agencies and brands to build or license their own buyer agents, potentially decentralizing how demand enters the ecosystem and making the sell side's role in enabling supply intelligence, curation, and scaled execution even more important.

Timeline

• October 15, 2025: Six companies launched Ad Context Protocol with founding members Scope3, Yahoo, PubMatic, Swivel, Triton Digital, and Optable
• October 15, 2025: Industry veteran David Kohl warned AdCP represents premature infrastructure development
• October 24, 2025: Magnite introduced machine learning-powered ad podding within SpringServe
• November 2, 2025: Industry skepticism emerged about AdCP protocol necessity
• November 3, 2025: Ari Paparo published analysis questioning AdCP media buying viability
• November 3, 2025: LiveRamp donated User Context Protocol to IAB Tech Lab
• November 4, 2025: Swivel launched agentic transaction capabilities for programmatic advertising
• November 5, 2025: Magnite reported Q3 2025 results with 18% CTV growth
• November 13, 2025: IAB Tech Lab introduced Agentic RTB Framework version 1.0 for public comment
• December 2025: Magnite ran first test with Scope3 serving as buyer agent
• December 2025: Industry experts debated AdCP viability and fraud concerns
• January 5, 2026: PubMatic launched AgenticOS with live campaigns running
• January 6, 2026: Magnite announced seller agent integration within SpringServe platform

Summary

Who: Magnite, the largest independent sell-side advertising platform, built a seller agent into its SpringServe platform. Publisher partners testing the system include LG Ad Solutions, MiQ, and Warner Bros. Discovery. Scope3 served as the buyer agent in December tests. Additional pilots involve multiple unnamed partners scheduled for early 2026.

What: Magnite embedded seller agent capabilities directly within SpringServe to support the Advertising Context Protocol, an open standard enabling AI agents to communicate campaign requirements, match inventory, and place campaigns. The seller agent allows publishers to engage in AdCP tests, modernize traditional buying methods through automation, collaborate with emerging buyer agents, and participate in defining agentic advertising standards.

When: Magnite announced the seller agent integration on January 6, 2026. The company ran its first test in December 2025 with Scope3 as buyer agent, with additional pilots lined up for early 2026. The broader AdCP protocol launched on October 15, 2025.

Where: The seller agent operates within SpringServe, Magnite's combined CTV ad serving and supply-side platform that maintains 99% coverage of US streaming supply. Initial testing involves major streaming platforms including those operated by Disney Advertising, LG Ad Solutions, Paramount, Roku, Samsung, and Warner Bros. Discovery.

Why: Magnite built the seller agent to position itself across any transaction rails buyers choose, whether programmatic, insertion order workflows, or emerging agent-driven channels. The company sees AdCP as a potential catalyst for more open, flexible, and efficient buying and selling, with AI lowering barriers for agencies and brands to build or license buyer agents that could decentralize demand entry. In a world where both buyers and sellers use agents, the sell side becomes more important for enabling supply intelligence, curation, and scaled execution.