import type { ApiInterfaceRx } from '@polkadot/api/types';
import type { BlockNumber } from '@polkadot/types/interfaces';
import type { Observable } from '@polkadot/x-rxjs';
/**
 * @name bestNumberFinalized
 * @returns A BlockNumber
 * @description Get the latest finalized block number.
 * @example
 * <BR>
 *
 * ```javascript
 * api.derive.chain.bestNumberFinalized((blockNumber) => {
 *   console.log(`the current finalized block is #${blockNumber}`);
 * });
 * ```
 */
export declare function bestNumberFinalized(instanceId: string, api: ApiInterfaceRx): () => Observable<BlockNumber>;