WebSocket Connections

Connecting to Sei via WebSocket for real-time block and event subscriptions

WebSocket Connections

Sei supports eth_subscribe over WebSocket. You can subscribe to new blocks, event logs, and pending transactions using standard library WebSocket transports.

Endpoints

Network	WebSocket endpoint
Mainnet	wss://evm-ws.sei-apis.com
Testnet	wss://evm-ws-testnet.sei-apis.com
Devnet	wss://evm-ws-arctic-1.sei-apis.com

Connecting

viem

import { createPublicClient, webSocket } from 'viem';
import { sei } from 'viem/chains';

const client = createPublicClient({
  chain: sei,
  transport: webSocket('wss://evm-ws.sei-apis.com'),
});

Watching New Blocks

viem

const unwatch = client.watchBlocks({
  onBlock: (block) => {
    console.log('New block:', block.number);
  },
});

// Stop watching
unwatch();

Watching Contract Events

viem

import { parseAbiItem } from 'viem';

const unwatch = client.watchEvent({
  address: '0xContractAddress',
  event: parseAbiItem('event Transfer(address indexed from, address indexed to, uint256 value)'),
  onLogs: (logs) => {
    console.log('Transfer events:', logs);
  },
});

Watching ERC-20 Transfers Across All Contracts

viem

import { parseAbiItem } from 'viem';

const unwatch = client.watchEvent({
  event: parseAbiItem('event Transfer(address indexed from, address indexed to, uint256 value)'),
  onLogs: (logs) => {
    logs.forEach((log) => {
      console.log(`Transfer on ${log.address}:`, log.args);
    });
  },
});

Notes

• Sei’s instant finality means every block emitted over WebSocket is already final — no need to wait for additional confirmations before acting on an event.
• Pending transaction subscriptions (newPendingTransactions) are supported at the RPC level but Sei does not guarantee Ethereum-style pending state visibility.

newHeads Under Autobahn Consensus

When a node runs under Autobahn consensus, eth_subscribe("newHeads") notifications are delivered from an in-process notifier that publishes committed-block headers directly, rather than from the legacy consensus event bus. Subscribers still only observe headers for fully committed blocks, but the header payload differs from the legacy path in a few ways:

• parentHash, receiptsRoot, and transactionsRoot are returned as zero hashes (0x0000…0000). The Autobahn block-execution path does not build a Tendermint-style hash chain, so there is no meaningful value to surface for these fields.
• stateRoot is sourced from the finalized block’s AppHash (the post-execution application hash), rather than from a pre-execution header field.
• hash is the Autobahn block-header hash — the same value reported as blockHash by eth_getBlockByNumber and the receipt APIs, keeping newHeads consistent with the rest of the EVM RPC surface.
• gasUsed is an approximation (summed from per-transaction results) to keep the notification cheap.

Because of these differences:

• Subscribers that chain-validate the head stream by linking parentHash values cannot rely on newHeads under Autobahn and need a different mechanism.
• If you need exact gasUsed or the omitted hash fields, fetch the block explicitly with eth_getBlockByNumber.