Flexible Transactions is a new technology that is still in testing and not available on the network. For information purposes this page explains what exactly needs to happen in order to start using FlexTrans in Bitcoin.
At its basis, Flexible Transactions is a new format that can be deployed
alongside anything we currently have.
This means that Flexible Transactions on the Bitcoin network will not cause any problems with value stored in old transactions. All old coins will continue to have value. Even things like n-lock-time based transactions people may have stored on their harddrive will continue to be valid.
FlexTrans uses the same addressing method that current transactions use. You can spend an old tx with a flextrans one and vice versa.
Thin Wallet users (SPV).
If you use a desktop application or one on your phone this is you. Also if you use a specific hardware wallet.
Flexible Transactions is fully backwards compatible as long as you personally don't actually receive a transaction of the new format. People only need to get a wallet that supports FlexTrans if they receive a Flexible Transaction or if they want to create one themselves. Users may want to create the new format because Flexible Transactions are smaller and have more features that make payments more secure.
When a user sends a old style transaction that spends a flextrans one to a user that does not have a flextrans wallet, that user will only get notified of the payment when the transaction gets mined. She will not get a notification before that.
The bitcoin full node has as the definition that it will validate all transactions and all blocks. As such this node software will have to be able to understand the FlexTrans format in order to validate it.
Mining pool operators.
This group is essentially the same as the full-node group.
Miners use special software to communicate with their mining pool operator. That software does not need to have any changes made for FlexTrans to work.