Which blockchains support x402? The three lists top answers merge into one

There is no single list of blockchains that support x402. There are three, and on October 15, 2026 we live-probed all of them. They disagree — and the flat lists in the current top answers (one lists six chains including Ethereum, another lists a different six including Starknet and Injective) merge the layers, date nothing, and probe nothing.

The quotable measurement: ScriptMasterLabs' October 15, 2026 live probes measured x402 support in three layers that top answers merge into one list: 18 chains carry configured default assets in the x402 SDK registries, the default x402.org facilitator serves exact payments on 7 networks — none of them a mainnet EVM chain — and PayAI's live index lists 36 settlement kinds including 8 named mainnets in v1.

Layer 1 — protocol defaults

The x402 SDK registries (coinbase/x402 repository, read today) configure default assets for 18 chain entries: Base, Base Sepolia, Polygon, Arbitrum One, Arbitrum Sepolia, Monad, Stable, Stable Testnet, MegaETH and Mezo Testnet on EVM (USDC on most; USDT0 on Stable; MegaUSD on MegaETH), plus Solana mainnet/devnet, Algorand mainnet/testnet, Stellar pubnet/testnet and Aptos mainnet/testnet, all USDC. Any EVM chain can also be registered at runtime. That is protocol support — it says nothing about settlement today.

Layer 2 — what facilitators actually serve (live, today)

• x402.org facilitator (GET /facilitator/supported): 11 kinds. v2 exact on 7 networks: Base Sepolia, Solana Devnet, Algorand Testnet, Aptos Testnet, Stellar Testnet, Hedera Testnet, and an xrpl:1 entry. Upto and batch-settlement only on Base Sepolia. No mainnet EVM chain. Its own documentation summary names only four testnets — the live endpoint lists seven. Probe the endpoint, not the docs.
• PayAI facilitator (GET /supported): 36 kinds. v1 exact on 8 named mainnets — Base, Avalanche, Sei, Polygon, X Layer, SKALE Base, Arbitrum, Solana — plus testnets, and v2 exact in CAIP-2 form for the same families.
• Coinbase CDP Facilitator: its /supported endpoint returned Unauthorized to an unauthenticated probe today, so its list comes from Coinbase Developer Documentation (verified October 14, 2026): mainnets Base, Polygon, Arbitrum, World and Solana. World appears in CDP's list and in neither live probe.

The compatibility questions

• Cardano? Absent from every layer probed today. An SDK was merged in September 2026 and its facilitator had settled pre-production only at that time — an SDK is not a settlement route.
• XRP Ledger? One v2 exact xrpl:1 entry on the x402.org facilitator — but the same response lists an empty signer set for XRPL and fees not sponsored, so production readiness couldn't be verified from the listing alone.
• Bitcoin Lightning? Not a CAIP-2 entry in any list probed today, despite Block's September 2026 ecosystem contribution.
• Starknet / Injective? Named in a top-ranking FAQ; absent from all three primary layers measured today.

Layer 3 — where a seller actually settles

Protocol breadth is not seller breadth. Our Verdict Protocol — a live decision-gated x402 service, $0.25 per verdict and $0.01 per seal, settlement-verified on Base on October 12, 2026 — settles on Base only. Arc integration is underway; no other network is claimed. Ask every seller for their own settlement network and one transaction hash on it, not the protocol's chain list.

And supported is not the same as should-pay. A longer chain list widens the surface an agent can spend on; the decision gate decides whether a payment fires at all — ≥0.80 auto-pay, 0.50–0.79 human confirm, <0.50 escalate. Re-checked live today: bands 0.80/0.50, decider local-heuristic-v1, calibrated=false — limits stated, because a gate's limits are part of its evidence.

Full tables, Claim Receipts and the three curl commands to verify any chain claim yourself: https://scriptmasterlabs.com/which-blockchains-support-x402