coinbase · phdargen · Mar 30, 2026 · Mar 30, 2026
diff --git a/go/.changes/unreleased/add-arbitrum-one-and-arbitrum-sepolia-default-stablecoin.yaml b/go/.changes/unreleased/add-arbitrum-one-and-arbitrum-sepolia-default-stablecoin.yaml
@@ -0,0 +1,2 @@
+kind: added
+body: Add Arbitrum One (chain ID 42161) and Arbitrum Sepolid (chain ID 421614) support with USDC as the default stablecoin
diff --git a/go/mechanisms/evm/constants.go b/go/mechanisms/evm/constants.go
@@ -76,6 +76,8 @@ var (
 	ChainIDMezoTestnet = big.NewInt(31611)
 	ChainIDStable      = big.NewInt(988)
 	ChainIDPolygon     = big.NewInt(137)
+	ChainIDArbOne      = big.NewInt(42161)
+	ChainIDArbSepolia  = big.NewInt(421614)
 
 	// Network configurations
 	// See DEFAULT_ASSET.md for guidelines on adding new chains
@@ -163,6 +165,27 @@ var (
 				Decimals: DefaultDecimals,
 			},
 		},
+
+		// Arbitrum One
+		"eip155:42161": {
+			ChainID: ChainIDArbOne,
+			DefaultAsset: AssetInfo{
+				Address:  "0xaf88d065e77c8cC2239327C5EDb3A432268e5831", // USDC on ArbOne
+				Name:     "USD Coin",
+				Version:  "2",
+				Decimals: DefaultDecimals,
+			},
+		},
+		// Arbitrum Sepolia
+		"eip155:421614": {
+			ChainID: ChainIDArbSepolia,
+			DefaultAsset: AssetInfo{
+				Address:  "0x75faf114eafb1BDbe2F0316DF893fd58CE46AA4d", // USDC on ArbSepolia
+				Name:     "USD Coin",
+				Version:  "2",
+				Decimals: DefaultDecimals,
+			},
+		},
 	}
 
 	// EIP-3009 ABI for transferWithAuthorization with v,r,s (EOA signatures)

diff --git a/...on/x402/changelog.d/add-arbitrum-one-and-arbitrum-sepolia-default-stablecoin.md b/...on/x402/changelog.d/add-arbitrum-one-and-arbitrum-sepolia-default-stablecoin.md
@@ -0,0 +1 @@
+Add Arbitrum One (chain ID 42161) and Arbitrum Sepolid (chain ID 421614) support with USDC as the default stablecoin
diff --git a/python/x402/mechanisms/evm/constants.py b/python/x402/mechanisms/evm/constants.py
@@ -353,6 +353,26 @@ class NetworkConfig(_NetworkConfigRequired, total=False):
             },
         },
     },
+    # Arbitrum One
+    "eip155:42161": {
+        "chain_id": 42161,
+        "default_asset": {
+            "address": "0xaf88d065e77c8cC2239327C5EDb3A432268e5831",
+            "name": "USD Coin",
+            "version": "2",
+            "decimals": 6,
+        },
+    },
+    # Arbitrum Sepolia
+    "eip155:421614": {
+        "chain_id": 421614,
+        "default_asset": {
+            "address": "0x75faf114eafb1BDbe2F0316DF893fd58CE46AA4d",
+            "name": "USD Coin",
+            "version": "2",
+            "decimals": 6,
+        },
+    },
 }
 
 # V1 legacy constants are in x402.mechanisms.evm.v1.constants

diff --git a/typescript/.changeset/add-arbitrum-one-and-arbitrum-sepolia-default-stablecoin.md b/typescript/.changeset/add-arbitrum-one-and-arbitrum-sepolia-default-stablecoin.md
@@ -0,0 +1,5 @@
+---
+"@x402/evm": patch
+---
+
+Add Arbitrum One (chain ID 42161) and Arbitrum Sepolid (chain ID 421614) support with USDC as the default stablecoin
diff --git a/typescript/packages/mechanisms/evm/src/shared/defaultAssets.ts b/typescript/packages/mechanisms/evm/src/shared/defaultAssets.ts
@@ -73,6 +73,18 @@ export const DEFAULT_STABLECOINS: Record<string, ExactDefaultAssetInfo> = {
     version: "2",
     decimals: 6,
   }, // Polygon mainnet USDC
+  "eip155:42161": {
+    address: "0xaf88d065e77c8cC2239327C5EDb3A432268e5831",
+    name: "USD Coin",
+    version: "2",
+    decimals: 6,
+  }, // Arbitrum One USDC
+  "eip155:421614": {
+    address: "0x75faf114eafb1BDbe2F0316DF893fd58CE46AA4d",
+    name: "USD Coin",
+    version: "2",
+    decimals: 6,
+  }, // Arbitrum Sepolia USDC
 };
 
 /**
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		kind: added
		body: Add Arbitrum One (chain ID 42161) and Arbitrum Sepolid (chain ID 421614) support with USDC as the default stablecoin
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Add Arbitrum One (chain ID 42161) and Arbitrum Sepolid (chain ID 421614) support with USDC as the default stablecoin