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Anycast addresses are taken from the unicast address space, and are not syntactically distinguishable from unicast addresses.

Anycast: An identifier for a set of interfaces (typically  belonging to different nodes). A packet sent to an anycast address is delivered to one of the interfaces identified by that address (the “nearest” one, according to the routing protocols’ measure of distance)
 
Watch how to configure IPv6 Anycast by clicking the image below
 

 

RFC2526  defines a set of reserved subnet anycast addresses. These are the highest 128 interface identifier values, within each subnet.  The syntax and rules for assigning new IPv6 reserved subnet anycast addresses are defined in this RFC.