eth_subscribe

eth_subscribe opens a push-based subscription over a WebSocket connection to Arbitrum One (chain ID 42161), the Optimistic Rollup that settles to Ethereum and pays gas in ETH. Instead of repeatedly polling the node, you register once and the node streams notifications as events occur — new block headers, matching logs, pending transaction hashes, or sync-status changes. Because Arbitrum's sequencer produces sub-second soft confirmations, a newHeads stream from wss://arbitrum.therpc.io/YOUR_API_KEY (the WebSocket form of the same endpoint you use for HTTP at https://arbitrum.therpc.io/YOUR_API_KEY) gives you the freshest possible view of L2 state without the latency and request overhead of polling loops.

Use cases

• Stream newHeads to drive real-time dashboards — block explorers, gas trackers, or TVL tickers — that react to each Arbitrum block the moment the sequencer publishes it, with no polling.
• Receive live logs events from a contract as they are included, for example Swap events from Camelot or Uniswap pools, or borrow/repay events from Aave, scoped by address and topics.
• Monitor newPendingTransactions to watch transactions enter the sequencer's mempool — useful for trade execution bots on GMX or for front-running-aware order flow analysis.

Parameters

Response

Example request

1curl https://arbitrum.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H "Content-Type: application/json" \
4  -d '{
5    "jsonrpc": "2.0",
6    "method": "eth_subscribe",
7    "params": [
8        "newHeads",
9        {}
10      ],
11    "id": 1
12  }'

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• Requires a WebSocket connection. Calling eth_subscribe over plain HTTP returns a "notifications not supported" error — point your client at the wss://arbitrum.therpc.io/YOUR_API_KEY form, not the HTTPS one.
• Events emitted while your connection is dropped are lost; the node does not replay them. Implement reconnect logic and backfill the gap with eth_getLogs over the missed block range so you do not silently skip Arbitrum events.
• logs notifications can arrive with removed: true during a reorganisation. While Arbitrum's sequencer rarely reorgs L2 ordering, your code must still handle removed events explicitly and unwind any state you derived from the superseded log.

Supported networks

• Mainnet — Chain ID: 42161
• Sepolia — Chain ID: 421614

See also

• eth_unsubscribe
• eth_newFilter
• eth_getLogs
• eth_getFilterChanges

1curl https://arbitrum.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H 'Content-Type: application/json' \
4  -d '{"jsonrpc":"2.0","id":1,"method":"eth_subscribe","params":["",null]}'