eth_subscribe

eth_subscribe opens a push-based subscription over a persistent WebSocket connection to OP Mainnet, the OP Stack optimistic rollup that settles to Ethereum L1 and pays gas in ETH. Instead of repeatedly polling for changes, you register interest in an event stream — new block headers, matching logs, pending transactions, or sync status — and the node pushes eth_subscription notifications the moment events occur. On a fast L2 with roughly 2-second blocks this is the difference between near-instant updates and wasted round trips. Connect over WebSocket at https://optimism.therpc.io/YOUR_API_KEY (chain ID 10, 0xa) and you receive a hex subscription ID to correlate the incoming stream.

Use cases

• Stream newHeads to drive real-time dashboards and block explorers that track OP Mainnet's ~2-second cadence without any polling loop.
• Subscribe to logs with an address/topics filter to react to events from a contract — for example Velodrome pool swaps or Synthetix events — the instant they are included in a block.
• Watch newPendingTransactions to observe transactions entering the sequencer's mempool before they are confirmed.

Parameters

Response

Example request

1curl https://optimism.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 Optimism playground.

Errors & troubleshooting

Common pitfalls

• Requires a WebSocket connection; calling eth_subscribe over a plain HTTP transport returns a "notifications not supported" error.
• Any events emitted while your connection is dropped are lost — there is no replay buffer. Implement reconnect logic and backfill the gap with eth_getLogs over the missed block range.
• Although OP Mainnet's sequencer produces a stable chain, logs notifications can still carry removed: true entries on rare reorgs near the unsafe head; handle these explicitly and only treat finalized data as settled once it is anchored on Ethereum L1.

Supported networks

• Mainnet — Chain ID: 10
• Sepolia — Chain ID: 11155420

See also

• eth_unsubscribe
• eth_newFilter
• eth_getLogs
• eth_getFilterChanges

1curl https://optimism.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]}'