Sponsor chains

Connection and deploy facts for the six chains with prize tracks at ETHGlobal Mumbai. Every chain ID below was confirmed against the chain's live public RPC on 19 Oct 2026. Testnets change: before deploying, confirm the chain ID and RPC on the official page linked in the reference.

Testnets at a glance

Mainnets, WebSockets, explorers, all faucets and Hardhat/Foundry snippets: references/chains.md.

Gotchas that break deploys

• 0G: the Galileo testnet is chain 16602. viem's older zeroGGalileoTestnet (16601) and zeroG (16600) exports are deprecated: use zeroGTestnet. Compile for the Cancun EVM version. The faucet gives 0.1 0G a day, so ask the team early if you need more.
• Arc: gas is paid in USDC. Native amounts use 18 decimals, but the USDC token contract uses 6 for the same balance. A transaction with a max fee below 20 gwei is dropped silently. PREVRANDAO is always 0, so don't use it for randomness.
• Hedera: over JSON-RPC, values use 18 decimals while native HBAR uses 8 (1 tinybar = 10^10 wei). Use an ECDSA account with an EVM alias for EVM work; ED25519 keys can't sign EVM transactions. A faucet-created account can't send until it's completed. Associate an HTS token before receiving it. Hashio is for development only.
• Whitechain: it is moving to an OP Stack L2 whose mainnet isn't live yet; build on Whitechain Sepolia (1874). Check eth_chainId rather than the RPC hostname. The faucet needs a GitHub account at least 30 days old and limits by IP, so claim before the event or from a phone hotspot, not the venue Wi-Fi.
• Unichain and World Chain: the public RPCs are rate limited. Use a provider key (Alchemy, QuickNode and others on the board) for anything that polls.

Using a chain with viem

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

const client = createPublicClient({ chain: unichainSepolia, transport: http() });
console.log(await client.getChainId()); // 1301

Swap in any export from the table. For Hardhat and Foundry config per chain, see references/chains.md.

About

Hand-written for Backboard, an independent project not affiliated with ETHGlobal or any of these chains. Checked against each chain's official docs on 19 Oct 2026 (sources are in the reference). When this and the official docs disagree, the docs win.