curl using socks5 proxy and IPv4

When using curl with socks5 proxy, seems that my IPv4 addressing is gone: $ env ALL_PROXY=socks5h://localhost:8001 curl -4 ipconfig.io 2607:xxxxxxxx:681f $ curl -4 ipconfig.io 97.xx.xx.116 What is the problem and how to ensure curl still uses IPv4 when using socks5 proxy?