I know 1 (P2PKH) and 3 (P2SH). But what is the "4" prefix?

4PXAyBiWgTo2EaNvxbpLz8d4edj2taEWux
4GY6DnSvHiGou5G9akzHrXvXqwyz5zmTSR
...

etc.

Blockchain.info says only "Unrecognized Address Version 8", but the blockchain parser finds (at least) like 650 of these addresses with funds on them.

Rico