The old Version 4 had a a limit of about 4000000000 addresses and as you see everyone uses a computer and they started running out of possible addresses to use so they came out with version 6 which can handle Approximately 300000000000000000000000000000000000000 different addresses to figure in growth for a good long while
It may be a few years till there is 100% version 6 switch over. When you get a new modem you will be using version 6 as simple as that.
They most likely want to get people to switch over to because its easier on them to give out addresses from the bigger v6 space.
Maybe you can get a complimentary modem upgrade if your leasing it, that may also boost your speeds a bit depending on how old your current one is.
