# API Updates

 * `lightning-block-sync`'s `UtxoSource` trait now fetches block txid lists
   (via `UtxoSource::get_block_txids`) rather than full blocks when verifying
   gossip against the chain, and `UtxoSource::is_output_unspent` was replaced
   by `UtxoSource::get_unspent_txout`, which additionally returns the output
   itself. This reduces the bandwidth required to validate network graph
   when using Bitcoin Core as a chain source. Custom implementations of
	 `UtxoSource` must implement the new methods.
