What are the differences between std::variant and boost::variant?

Question

In an answer to this SO question:

What is the equivalent of boost::variant in the C++ standard library?

it is mentioned that boost::variant and

Answer 1

It seems the main point of contention regarding the design of a variant class has been what should happen when an assignment to the variant, which should upon completion destory the old value, throws an exception:

variant v = "ABC";
v = MyClassWithThrowingDefaultCtor();

The options seem to be:

• Prevent this by restricting the possible representable types to nothrow-move-constructible ones.
• Keep the old value - but this requires double-buffers (which is what boost::variant does apparently).
• Have a 'disengaged' state with no value for each variant, and go to that state on such failures.
• Undefined behavior
• Make the variant throw when trying to read its value after something like that happens

and if I'm not mistaken, the latter is what's been accepted.

_{This is summarized from the ISO C++ blog post by Axel Naumann from Nov 2015.}