Circle's Stack framework names identity, value-transfer, and settlement as the Foundation layer of an open agent economy. This collection meshes that thesis with the x402-buyer skill, a real reference implementation, and reports what happened when the Foundation layer's value-transfer claim met live infrastructure — including one independently on-chain-verified settlement.
Circle's “Building the Open Agentic Economy” argues that intelligence is becoming the internet's next foundational building block — software as delegable labor that monetizes its own work, provided agents can discover, install, and pay for services without gatekeepers. It proposes a three-layer Stack (Foundation, Trust Primitives, Capstone) and five principles for trusted discovery.
The x402-buyer skill is a working implementation of exactly the Foundation layer's value-transfer component: a client that fetches a URL, signs a real EIP-3009 authorization when challenged with HTTP 402, and settles against the public Base Sepolia facilitator. This collection doesn't just summarize Circle's thesis — it tests one specific claim against it, using three probes run in the same session that generated this document, one of which completed a genuine, independently-verified on-chain settlement.
Circle's own three-layer status model, in order — existing, emerging, missing.
Circle invokes PageRank (1998) and warns that self-declared onchain feedback “can be cheap to game” — hence a discovery layer grounded in observed behavior, not self-description.
Three live probes run against real, independently-operated OpenLink resource servers using x402-buyer as a reference implementation of the Foundation layer's value-transfer component, authored by the kg-generator skill on the curating principal's behalf.
The client reported success with a transaction hash. That claim was not taken at face value: a direct eth_getTransactionReceipt RPC call to the same public Base Sepolia endpoint the skill defaults to confirmed status 0x1, a matching ERC-20 Transfer event, and the exact settled amount — buyer 0x0102257D…2ab553 to seller 0xb410b5E8…1200C79, tx 0x2efb8442…90f4144.
WebID-TLS/NetID-TLS on these resource servers lives on port 5443, not 443 — port 443 never issues a CertificateRequest, so it falls straight through to a misleading 401 regardless of certificate availability. A naive first attempt at reaching a Foundation-layer resource would conclude, wrongly, that it has no payment layer at all. Confirmed identical behavior on two independent hosts, and generalized into both x402-buyer and acp-client as an automatic default the same session.
SELECT DISTINCT ?s AS ?sampleEntity (COUNT(*) AS ?entityCount) ?o AS ?EntityType
WHERE { ?s a ?o }
ORDER BY DESC(?entityCount) LIMIT 50Run against urn:jch:test on ods-qa.openlinksw.com — the exact query behind the SPARQL-endpoint decode evidence above.
Run live query
Interactive graph visualization derived from the companion RDF. Click nodes to resolve, drag to explore. Graph data embedded from companion RDF at generation time.
Choose a named graph and query recipe, edit the SPARQL if needed, then open the encoded URIBurner query.
SELECT uses text/x-html+tr. DESCRIBE and CONSTRUCT use text/x-html-nice-turtle, matching the SPARQL format guidance in the skill contract.
A 401 with WWW-Authenticate: Digest on port 443 is NOT proof the resource lacks an x402 layer.
This is where the CertificateRequest is actually issued; x402-buyer automates the port rewrite.
Some resources 302-redirect through a ?k=... capability URL before the real 402; others answer directly.
Base64-decode the challenge to see the amount, network, and pay-to address before any signing happens.
Run x402-buyer's scripts/x402_get.py, which signs a real EIP-3009 authorization.
Query the same public RPC endpoint directly for the transaction receipt — never rely on the client's self-report alone.
That intelligence is becoming the internet's next foundational building block, turning software into delegable labor that can monetize its own work.
A three-layer model: Foundation (existing), Trust Primitives (emerging), Capstone (missing).
The value-transfer protocol component, alongside ERC-8004, OpenAPI/agentURI, and USDC settlement.
A payment protocol activating HTTP's reserved 402 status code for per-request stablecoin settlement.
Organic rank never for sale; permissionless inclusion; open read surface; contestable ranking; ranking is not adjudication.
Research it cites suggests it can be cheap to game, so multiple behavior-grounded inputs are needed instead.
Three live probes: two decoded challenges ($2.99, $4.99) and one fully signed, settled, on-chain-verified payment ($9.99).
A direct eth_getTransactionReceipt RPC call confirming status, the ERC-20 Transfer event, and the exact amount.
WebID-TLS/NetID-TLS lives on port 5443, not 443 — a naive attempt would see a misleading 401 and conclude wrongly.
A 2025 Ethereum Improvement Proposal defining a Trustless Agents identity standard plus reputation/validation registries.
99.3%, as of 2026-07-31, alongside $90.8 trillion cumulative onchain USDC volume as of 2026-07-07.
A curated catalog of 900+ paid services with a public discovery API; agents call services without account creation.
A developer publishes a paid agent; an independent buyer with no prior relationship discovers, prices, and transacts with it.
No — the Empirical Validation section is agent-synthesized commentary, structurally separate and not attributed to Circle.
A payment protocol activating HTTP's reserved 402 status code for per-request stablecoin settlement.
Machine/Monetary Payment Protocol — x402's sibling protocol family in Circle's Foundation layer.
Circle's US-dollar-pegged stablecoin, the dominant settlement asset in x402 transactions.
An Ethereum Improvement Proposal defining a Trustless Agents identity standard and trust registries.
A mutual-TLS protocol binding a client certificate to a WebID; on OpenLink servers, lives on port 5443.
Alias/successor naming for WebID-TLS used interchangeably — same underlying mTLS mechanism.
The third party that verifies and settles a presented x402 payment authorization on-chain.
An Ethereum token-transfer authorization standard the x402-buyer skill signs to authorize settlement.
A gasless-approval mechanism some x402 challenges advertise as an extension.
The base64-encoded HTTP header carrying an x402 challenge's accepts[] options.
The Ethereum Layer-2 testnet this session's x402 probes and settlement ran against.
Circle's bar for its Full Loop milestone: a transaction between parties with no prior relationship.