So 10.1 is the version that includes all updates necessary for the next hardfork in january 2017.
But as far as i understood the hardfork cycle, one version below the hardfork version will still work or?
For example could i still run version 10 after the january 2017 hardfork? What about version 9.4? Would it also work and how long would it work?
10.1 has a fix for RingCT. Changes have been made to 10.1 nodes to fork one block before 10.0 in order to avoid letting anyone use the flawed RingCT code, so Miners need to make sure they mine on 10.1 as they need to make sure they include the bugfixed RingCT transactions only, otherwise they will fork themselves off the network. The code changes that result in this is shown here
In short, the wallet software can be used until september 2017, but the node software MUST be upgraded (most importantly miners) otherwise the nodes running 10.0 or earlier will no longer be visible on the fixed chain.
RingCT is optional in the January hard fork, it only becomes mandatory as of the September, 2017, hard fork. Thus, if you continue to run a 10.0 node you will stay on the network until the first RingCT transaction, at which point you'd fork off as your node doesn't understand the RingCT changes.
However, you will be able to use a 10.0 wallet up until September 2017, as the non-RingCT transactions it creates are perfectly fine.
