(IPv6 doesn't fragment, but guarantees a minimum MTU of 1200 bytes)
I mean that the intervening nodes (routers) will not do fragmentation -- there's nothing preventing an IPv6 software stack on the sending end to implement this before it hits the network.
It is possible for the sending node to do path MTU discovery and use the Fragment extension. This is possible for an intermediate software layer to do, to support larger UDP datagrams, rather than limit the size of UDP datagrams. The way I read the spec, this is "strongly recommended" but not guaranteed.