BlockRunAI · VickyXAI · Sep 16, 2026 · Sep 16, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -2,6 +2,31 @@
 
 All notable changes to blockrun-llm will be documented in this file.
 
+## 1.17.0 — 2026-09-16
+
+### Added
+- **Arc.** `LLMClient(api_url="https://arc.blockrun.ai/api")` pays on Circle's
+  Arc. The chain table knew Base and Base Sepolia and fell back to Base for
+  anything else, while `asset` and `extra` were taken from the 402 as given —
+  so against arc.blockrun.ai (`eip155:5042`, USDC at `0x3600…`, domain name
+  `USDC`) every payment was a signature over chainId 8453 with Arc's contract:
+  invalid, a 401 from the facilitator, after the SDK had reported a payment.
+
+  `EVM_NETWORKS` in `blockrun_llm.x402` maps a 402's `network` to the SDK's
+  own chain id, USDC address and EIP-712 domain (Base, Arc, Base Sepolia; the
+  `base-sepolia` alias still resolves). The 402 selects the network and
+  supplies nothing else: its `extra` no longer reaches the domain, an unknown
+  network raises `ValueError` naming what is supported, and a 402 whose
+  `asset` is not that network's USDC raises before anything is signed. Every
+  EVM client passes the 402's `asset` through. `accepted.asset` and
+  `accepted.extra` in the payload now describe the network actually signed.
+  Mirrors `@blockrun/llm` 3.16.0.
+
+  Verified against arc.blockrun.ai with an unfunded throwaway key: Circle's
+  `/verify` answers `insufficient_funds` and recovers the throwaway's own
+  address as `payer` — the signature verifies on Arc's domain; only the
+  balance is missing.
+
 ## 1.16.0 — 2026-09-08
 
 ### Fixed

diff --git a/CLAUDE.md b/CLAUDE.md
@@ -18,7 +18,7 @@ mypy blockrun_llm/                # type check
 ```
 blockrun_llm/
 ├── __init__.py              # Package exports
-├── client.py                # LLMClient (Base chain)
+├── client.py                # LLMClient (EVM: Base, Arc — the 402's network picks the chain)
 ├── solana_client.py         # SolanaLLMClient
 ├── wallet.py                # EVM wallet management
 ├── solana_wallet.py         # Solana wallet management
@@ -51,9 +51,12 @@ blockrun_llm/
 ## Supported chains
 
 - Base Mainnet (primary) — USDC
+- Arc (Circle, chain 5042) — USDC, via `api_url="https://arc.blockrun.ai/api"`; same `LLMClient` and key
 - Base Sepolia (testnet) — Testnet USDC
 - Solana Mainnet — USDC SPL
 
+The EVM domain signed follows the 402's `network` through `EVM_NETWORKS` in `blockrun_llm/x402.py`; a 402's `extra` is never trusted for it, an unknown network and a non-USDC `asset` are refused.
+
 ## Conventions
 
 - Python >= 3.9

diff --git a/README.md b/README.md
@@ -22,6 +22,7 @@
 | **API key** | none — `api.blockrun.ai` | prepaid credit, topped up with a card | ✅ |
 | **Solana** | Solana Mainnet | USDC (SPL), gasless — the facilitator pays the fee | ✅ Recommended for x402 |
 | **Base** | Base Mainnet (Chain ID: 8453) | USDC | ✅ |
+| **Arc** | Circle Arc (Chain ID: 5042) — `arc.blockrun.ai` | USDC (Arc's native token), settled by Circle — no gas per call | ✅ |
 | **Base Testnet** | Base Sepolia (Chain ID: 84532) | Testnet USDC | ✅ Development |
 
 **Protocol:** x402 v2 on the wallet rails; plain bearer auth on the API-key rail.
@@ -151,6 +152,24 @@ export SOLANA_WALLET_KEY="your-bs58-solana-key"
 > what to switch to instead of failing with a cryptic "must be 66 characters"
 > error.
 
+## Arc Support
+
+The same `LLMClient` pays on [Circle's Arc](https://www.arc.network) via [arc.blockrun.ai](https://arc.blockrun.ai) — point `api_url` at it and hold USDC on Arc in the same EVM wallet:
+
+```python
+from blockrun_llm import LLMClient
+
+client = LLMClient(api_url="https://arc.blockrun.ai/api")  # BLOCKRUN_WALLET_KEY as usual
+print(client.chat("openai/gpt-4o", "gm Arc"))
+```
+
+The 402 from that host names `eip155:5042`, and the SDK signs the EIP-3009 authorization against Arc's USDC (`0x3600…0000`, EIP-712 domain `USDC` v2) — never Base's. Circle's facilitator verifies and settles it on Arc; you pay no gas. Which networks the SDK can sign for is the `EVM_NETWORKS` table in `blockrun_llm.x402` (Base, Arc, Base Sepolia); a 402 naming any other network, or a non-USDC asset, is refused before anything is signed.
+
+**Setup:**
+1. Same wallet key as Base: `export BLOCKRUN_WALLET_KEY="0x..."`
+2. Fund it with USDC on Arc (Arc's native token, shown as the ERC-20 at `0x3600…0000`)
+3. `api_url="https://arc.blockrun.ai/api"` — payments are automatic via x402
+
 ## Smart Routing (Router Core)
 
 Let the SDK automatically pick the cheapest capable model for each request:

diff --git a/VERSION b/VERSION
@@ -1 +1 @@
-1.16.0
+1.17.0
diff --git a/blockrun_llm/__init__.py b/blockrun_llm/__init__.py
@@ -196,7 +196,7 @@
     create_wallet as generate_wallet,  # User-friendly alias
 )
 
-__version__ = "1.16.0"
+__version__ = "1.17.0"
 __all__ = [
     "DEFAULT_API_KEY_URL",
     "ENV_API_KEY",

diff --git a/blockrun_llm/image.py b/blockrun_llm/image.py
@@ -369,6 +369,7 @@ def _handle_payment_and_retry(
             resource_description=resource.get("description", "BlockRun Image Generation"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/music.py b/blockrun_llm/music.py
@@ -257,6 +257,7 @@ def _handle_payment_and_retry(
             resource_description=resource.get("description", "BlockRun Music Generation"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/phone.py b/blockrun_llm/phone.py
@@ -299,6 +299,7 @@ def _handle_payment_and_retry(
             resource_description=resource.get("description", "BlockRun Phone"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/portrait.py b/blockrun_llm/portrait.py
@@ -289,6 +289,7 @@ def _handle_payment_and_retry(
             ),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/price.py b/blockrun_llm/price.py
@@ -305,6 +305,7 @@ def _pay_and_retry(
             resource_description=resource.get("description", "BlockRun Price Data"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/realface.py b/blockrun_llm/realface.py
@@ -441,6 +441,7 @@ def _handle_payment_and_retry(
             resource_description=resource.get("description", "BlockRun RealFace Enrollment"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/rpc.py b/blockrun_llm/rpc.py
@@ -385,6 +385,7 @@ def _handle_payment_and_retry(
             resource_description=resource.get("description", "BlockRun Multi-chain RPC"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/search.py b/blockrun_llm/search.py
@@ -205,6 +205,7 @@ def _handle_payment_and_retry(
             resource_description=resource.get("description", "BlockRun Search"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/speech.py b/blockrun_llm/speech.py
@@ -336,6 +336,7 @@ def _handle_payment_and_retry(
             resource_description=resource.get("description", "BlockRun Voice"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/surf.py b/blockrun_llm/surf.py
@@ -390,6 +390,7 @@ def _handle_payment_and_retry(
             resource_description=resource.get("description", "BlockRun Surf"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/video.py b/blockrun_llm/video.py
@@ -522,6 +522,7 @@ def _sign_from_challenge(self, resp402: httpx.Response, fallback_url: str) -> st
                 details.get("maxTimeoutSeconds", 0) or 0, self.MAX_TIMEOUT_SECONDS
             ),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/voice.py b/blockrun_llm/voice.py
@@ -348,6 +348,7 @@ def _handle_payment_and_retry(
             resource_description=resource.get("description", "BlockRun Voice Call"),
             max_timeout_seconds=details.get("maxTimeoutSeconds", 300),
             extra=details.get("extra"),
+            asset=details.get("asset"),
             extensions=extensions,
         )
 

diff --git a/blockrun_llm/x402.py b/blockrun_llm/x402.py
@@ -24,6 +24,68 @@
 BASE_SEPOLIA_CHAIN_ID = 84532
 USDC_BASE_SEPOLIA = "0x036CbD53842c5426634e7929541eC2318f3dCF7e"
 
+# Circle's Arc (arc.blockrun.ai). USDC is the chain's native token, exposed as
+# the ERC-20 at 0x3600…0000; its EIP-712 domain name is "USDC", not Base's
+# "USD Coin".
+ARC_CHAIN_ID = 5042
+USDC_ARC = "0x3600000000000000000000000000000000000000"
+
+# The EVM networks a BlockRun gateway settles on, keyed by the CAIP-2 `network`
+# a 402 carries, each with the SDK's OWN chain id, USDC address and EIP-712
+# domain. The 402 SELECTS a network from this table; it never supplies the
+# domain — until the Arc release the table fell back to Base for any network
+# it did not know and took `asset` and `extra` from the 402 as given, which on
+# arc.blockrun.ai signed chainId 8453 against Arc's contract: an invalid
+# signature, a 401 from the facilitator, after the SDK had reported a payment.
+EVM_NETWORKS: dict[str, dict] = {
+    "eip155:8453": {
+        "name": "Base",
+        "chain_id": BASE_CHAIN_ID,
+        "usdc": USDC_BASE,
+        "domain": {
+            "name": "USD Coin",
+            "version": "2",
+            "chainId": BASE_CHAIN_ID,
+            "verifyingContract": USDC_BASE,
+        },
+    },
+    "eip155:5042": {
+        "name": "Arc",
+        "chain_id": ARC_CHAIN_ID,
+        "usdc": USDC_ARC,
+        "domain": {
+            "name": "USDC",
+            "version": "2",
+            "chainId": ARC_CHAIN_ID,
+            "verifyingContract": USDC_ARC,
+        },
+    },
+    "eip155:84532": {
+        "name": "Base Sepolia",
+        "chain_id": BASE_SEPOLIA_CHAIN_ID,
+        "usdc": USDC_BASE_SEPOLIA,
+        "domain": {
+            "name": "USDC",
+            "version": "2",
+            "chainId": BASE_SEPOLIA_CHAIN_ID,
+            "verifyingContract": USDC_BASE_SEPOLIA,
+        },
+    },
+}
+# The pre-CAIP alias this SDK accepted for the testnet.
+_NETWORK_ALIASES = {"base-sepolia": "eip155:84532"}
+
+
+def evm_network(network: str) -> dict:
+    """The table entry for a 402's `network`, or a ValueError naming what IS supported."""
+    net = EVM_NETWORKS.get(_NETWORK_ALIASES.get(network, network))
+    if net is None:
+        raise ValueError(
+            f'Unsupported x402 network "{network}": this SDK signs USDC payments on '
+            + ", ".join(EVM_NETWORKS)
+        )
+    return net
+
 
 # BlockRun's x402 builder code — the ERC-8021 Schema 2 service code (`s`) that
 # tags every payment this SDK signs as BlockRun-originated for on-chain
@@ -50,36 +112,14 @@ def with_builder_code_service_code(
 
 
 def get_chain_config(network: str) -> tuple[int, str]:
-    """
-    Get chain ID and USDC contract address for a given network.
-
-    Args:
-        network: Network identifier in EIP-155 format (e.g., "eip155:8453" or "eip155:84532")
-
-    Returns:
-        Tuple of (chain_id, usdc_address)
-    """
-    if network == "eip155:84532" or network == "base-sepolia":
-        return BASE_SEPOLIA_CHAIN_ID, USDC_BASE_SEPOLIA
-    # Default to mainnet
-    return BASE_CHAIN_ID, USDC_BASE
+    """Chain ID and USDC contract for a network — see EVM_NETWORKS. Raises for an unknown one."""
+    net = evm_network(network)
+    return net["chain_id"], net["usdc"]
 
 
 def get_usdc_domain_name(network: str) -> str:
-    """
-    Get the EIP-712 domain name for USDC on a given network.
-
-    Mainnet USDC uses "USD Coin", testnet USDC uses "USDC".
-
-    Args:
-        network: Network identifier in EIP-155 format
-
-    Returns:
-        The EIP-712 domain name for signing
-    """
-    if network == "eip155:84532" or network == "base-sepolia":
-        return "USDC"
-    return "USD Coin"
+    """The EIP-712 domain name for USDC on a network — "USD Coin" on Base, "USDC" on Arc and Base Sepolia."""
+    return evm_network(network)["domain"]["name"]
 
 
 def create_nonce() -> str:
@@ -113,8 +153,8 @@ def create_payment_payload(
         resource_url: URL of the resource being accessed
         resource_description: Description of the resource
         max_timeout_seconds: Max timeout for the payment (default: 300)
-        extra: Extra info for USDC domain (name, version)
-        asset: USDC contract address (optional, derived from network if not provided)
+        extra: The 402's `extra`. Accepted for compatibility; the domain comes from EVM_NETWORKS.
+        asset: The 402's `asset`. Checked against the network's USDC; a mismatch raises ValueError.
 
     Returns:
         Base64-encoded signed payment payload
@@ -127,20 +167,17 @@ def create_payment_payload(
     # Generate random nonce
     nonce = create_nonce()
 
-    # Get chain config based on network
-    chain_id, default_usdc = get_chain_config(network)
-
-    # Use provided asset address or default for the network
-    usdc_address = asset or default_usdc
-
-    # EIP-712 domain for USDC (mainnet or testnet based on network)
-    default_domain_name = get_usdc_domain_name(network)
-    domain = {
-        "name": extra.get("name", default_domain_name) if extra else default_domain_name,
-        "version": extra.get("version", "2") if extra else "2",
-        "chainId": chain_id,
-        "verifyingContract": usdc_address,
-    }
+    # The domain is the SDK's own value for the 402's network — never the 402's
+    # `extra` (see EVM_NETWORKS). A 402 naming a network the table lacks, or an
+    # asset that is not that network's USDC, is refused rather than signed.
+    net = evm_network(network)
+    usdc_address = net["usdc"]
+    if asset and asset.lower() != usdc_address.lower():
+        raise ValueError(
+            f"x402 asset mismatch: the 402 asks for {asset} on {network}, "
+            f"but this SDK only pays USDC there ({usdc_address})"
+        )
+    domain = dict(net["domain"])
 
     # EIP-712 types for TransferWithAuthorization
     types = {
@@ -183,7 +220,7 @@ def create_payment_payload(
             "asset": usdc_address,
             "payTo": recipient,
             "maxTimeoutSeconds": max_timeout_seconds,
-            "extra": extra or {"name": default_domain_name, "version": "2"},
+            "extra": {"name": domain["name"], "version": domain["version"]},
         },
         "payload": {
             "signature": (

diff --git a/pyproject.toml b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "blockrun-llm"
-version = "1.16.0"
+version = "1.17.0"
 description = "BlockRun SDK - Pay-per-request AI (LLM, Image, Video, Music, Voice) via x402 on Base and Solana"
 readme = "README.md"
 license = "MIT"