OP Sepolia RPC Endpoint

Chain ID 11155420. OP Mainnet's testnet, the reference OP Stack chain, settling to Ethereum Sepolia.

Online right now, checked every 2 minutes. WebSocket: available.

Endpoints

https://rpc.swiftnodes.io/rpc/optimism-sepolia?key=YOUR_API_KEY
wss://rpc.swiftnodes.io/ws/optimism-sepolia?key=YOUR_API_KEY

The same API key works here and on Optimism mainnet, and testnet requests count toward your plan like any other request. The free plan includes testnets. Going to mainnet means changing optimism-sepolia to optimism in the URL.

import { createPublicClient, http } from "viem";
import { optimismSepolia } from "viem/chains";

const client = createPublicClient({
  chain: optimismSepolia,
  transport: http("https://rpc.swiftnodes.io/rpc/optimism-sepolia?key=YOUR_API_KEY"),
});

console.log(await client.getBlockNumber());

About OP Sepolia

OP Sepolia is the testnet for OP Mainnet and the reference chain for the OP Stack, the software behind Base, Unichain, Ink and many other L2s. OP Stack upgrades usually reach it before they reach OP Mainnet.

It produces a block every 2 seconds and settles to Ethereum Sepolia, with the same unsafe, safe and finalized heads as other OP Stack chains.

What we measured

Measured through our endpoint on October 18, 2026.

Chain ID	11155420 (0xaa37dc)
Block 1	August 12, 2023
Block interval	2.00 s over 200 blocks
Block gas limit	40,000,000
eth_gasPrice	0.001 gwei
safe / finalized	21 and 488 blocks behind the head

Frequently asked questions

What is the OP Sepolia chain ID?

11155420, or 0xaa37dc in hex.

Is OP Sepolia the same as Optimism Sepolia?

Yes. Optimism renamed its mainnet to OP Mainnet and the testnet is OP Sepolia; older docs call it Optimism Sepolia.

Is the OP Sepolia RPC endpoint free?

Yes. The free plan covers OP Sepolia at 20 requests per second and 250,000 requests a month, on the same key as OP Mainnet.

Other testnets

Get a free OP Sepolia endpoint

One key for every testnet and mainnet we serve. No credit card, no KYC.

Get your API key