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Compose comes with built in chain support for over 100 EVM chains, powered by our own “RPC Edge” product for ultimate RPC reliability. You can access all the built-in chains with evm.chains.<<chainName>>. Additionally, compose supports custom chain configurations. See Wallets and Smart Contracts for more details on how chains are used.

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Using built-in chains

This is the easiest and most reliable option for most scenarios. 
import { TaskContext } from "compose";

export async function main({ evm }: TaskContext) {
  // the "chains" object is typed and holds all our current natively supported chains
  // native chains are pre-configured to use goldsky's "edge" rpc technology
  console.log(evm.chains.base);
}

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Using custom chains

To use a custom chain you just need to create an object that fulfills our Chain interface. 
import { TaskContext, Chain } from "compose";

export async function main({ evm, env }: TaskContext) {
  // custom chain spec
  const myCustomChain: Chain = {
    id: 480,
    name: "My Custom Chain",
    testnet: false,
    nativeCurrency: { name: "Ether", symbol: "ETH", decimals: 18 },
    rpcUrls: {
      default: { http: [`https://mycustomchain-mainnet.g.alchemy.com/v2/${env.MY_CUSTOM_CHAIN_API}`] },
      public: { http: ["https://mycustomchain-mainnet.g.alchemy.com/public"] },
    },
    blockExplorers: {
      default: { name: "myCustomChainScan", url: "https://myCustomChainScan.org" },
    },
  };

  // you can now use the myCustomChain const anywhere you'd use a built-in chain (see Wallets and Smart Contracts for details)
  console.log(myCustomChain);
}
The Chain type is available from the TaskContext interface. Here it is for reference: 
export type Chain = {
  id: number;
  name: string;
  testnet: boolean;
  nativeCurrency: {
    name: string;
    symbol: string;
    decimals: number;
  };
  rpcUrls: {
    public: { http: string[] };
    default: { http: string[] };
  };
  blockExplorers: {
    default: { name: string; url: string };
  };
  contracts?: Record<string, { address: string }>;
};