​

WebSocket connections

​

Endpoints

​

Connecting

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

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

import { ethers } from 'ethers';

const provider = new ethers.WebSocketProvider('wss://evm-ws.sei-apis.com');

​

Watching new blocks

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

// Stop watching
unwatch();

provider.on('block', (blockNumber) => {
  console.log('New block:', blockNumber);
});

// Stop watching
provider.off('block');

​

Watching contract events

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);
  },
});

import { ethers } from 'ethers';

const ERC20_ABI = ['event Transfer(address indexed from, address indexed to, uint256 value)'];
const contract = new ethers.Contract('0xContractAddress', ERC20_ABI, provider);

contract.on('Transfer', (from, to, value, event) => {
  console.log('Transfer:', { from, to, value });
});

// Stop watching
contract.off('Transfer');

​

Watching ERC-20 transfers across all contracts

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 has instant finality, so every block emitted over WebSocket is already final. You do not need to wait for more confirmations before you act on an event.
• Pending transaction subscriptions (newPendingTransactions) are supported at the RPC level, but Sei does not guarantee Ethereum-style pending state visibility.

​

Frame size and concurrency limits

​

Frame size (max_request_body_bytes)

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Concurrent request budget (max_concurrent_request_bytes and ws_admission_timeout)

​

newHeads under Autobahn consensus

• 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 return in these fields.
• stateRoot comes from the finalized block’s AppHash (the post-execution application hash), not from a pre-execution header field.
• hash is the Autobahn block-header hash. It is the same value that eth_getBlockByNumber and the receipt APIs report as blockHash. This keeps newHeads consistent with the rest of the EVM RPC surface.
• gasUsed is an approximation (summed from per-transaction results) that keeps the notification cheap.

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