A subnet (i.e. a layer 2 network) always gets a /64 in IPv6; so the actual address space available for layer 3 routing is 64 bits.
The point of this ridiculously large space is that it makes routing tables smaller, because topologically-near areas can be given common prefixes without worrying about address exhaustion.
The point of this ridiculously large space is that it makes routing tables smaller, because topologically-near areas can be given common prefixes without worrying about address exhaustion.