Path MTU and UDP

An application sends a 4000-byte UDP datagram over a path with a 1500-byte MTU. What happens?

The datagram is silently truncated to 1500 bytes

UDP rejects the send and returns an error to the application

The IP layer fragments the datagram into multiple IP packets, which are reassembled at the destination before being delivered to UDP

UDP automatically splits the data into multiple separate datagrams