Agent ad formats: sponsored lines, host-rendered cards, and what comes next

Display advertising spent thirty years inventing formats — banners, interstitials, natives, rewarded video. Agent advertising is at day one of that curve, and the constraint driving it is beautiful: the publisher doesn't own the screen. The host model does.

Live today

The sponsored line. One labeled string with a link, attached as data to a tool response. The host weaves it in or ignores it. This is the format our whole contract is built around — it works in every host that can read a tool result, which is all of them.

The host-rendered card. When the host supports richer affordances (MCP Apps, structured content), the same labeled data renders as a card — title, description, link. Claude already does this on its own judgment. Same data, better clothes.

The suffix. For runtimes that own their response surface — WhatsApp bots, Telegram agents, self-hosted assistants — a deterministic, disclosed one-liner appended by the harness after generation. Never by the model, never as an instruction.

Coming as hosts add affordances

Interactive cards with actions ("book", "compare"), inline comparison rows for shopping-shaped queries, and audio-native disclosures for voice agents. Each becomes possible the moment a host exposes the affordance — our job is keeping the data contract stable underneath.

The rule that never changes

Whatever the format: the payload is data, the label is immutable, and the host decides. A format that requires instructing the model to display something isn't a format — it's an exploit with a rate card, and it dies the day the host notices. We only build the kind that survives.