From Evangelical Arminians:

So what exactly are Open Theists adding to libertarian free will? Open Theists hold the idea that propositions about future free will acts, in an absolute sense, cannot be true. (I say in an absolute sense, because some Open Theists reinterpret statements about the future in a relative, probabilistic sense, meaning given current factors, Bob will choose chocolate is more likely than not, but not 100% certain). If the statement, “Bob will eat chocolate” is true, then Bob is not free with respect to eating chocolate. Propositions about events become true the moment the events happen and not before. Bob himself has the power to change the proposition “Bob chose chocolate” from possibly true to actually true. This is how Open Theists cash out the idea of Bob making statements true and this is the power that Open Theists add to definition of libertarian free will.