One optional field, six steps, nothing hidden
AI agents are starting to pay each other through open payment protocols. This is a sketch of one optional extension: the owner agrees once, each payment carries a small solidarity share, and the money reaches crises by a rule anyone can check. Step through one purchase.
What the field can never do
Be switched on by anyone but the owner
A merchant, a marketplace or the agent itself cannot add it. It only rides on payments whose owner has a standing policy.
Pass the owner's cap
The policy carries a monthly ceiling. When it is reached, the field stops appearing until next month.
Tell the fund what you bought
Processors send totals and a fingerprint of their batch, never purchases. The fund learns how much, not what.
Go anywhere the rule does not say
The fund publishes its inputs and its rule before it pays. Anyone can rerun the allocation and get the same numbers.
Where it would fit
Three open efforts already define how agents pay: Google's Agent Payments Protocol (AP2), Coinbase's x402, which revives the web's long-unused "402 Payment Required" status, and the Agentic Commerce Protocol from OpenAI and Stripe. Each has room for extensions. The field sketched here is not part of any of them. The draft below is written against x402's actual extension mechanism, because it is published and specific; card and bank rails would carry the same fields in a processor's own API.
Draft spec: the solidarity extension, written against x402 v2 (its extension mechanism, the facilitator's EXTENSION-RESPONSES side channel, and RFC 6962 batches), with a JSON Schema and open questions for the maintainers.
Sources: TechCrunch on AP2, a comparison of AP2, x402 and ACP.