I first created the 8 network subnet /67 block.   I next configuration is to create a 16 network subnet with a /68 block.  

IPv6
Status Available
Global Unicast IPv6 Address 2600:1702:980:25e0::1
Link-local IPv6 Address fe80::eea:c9ff:feb8:84e0
IPv6 Addressing Subnet (including length) 2600:1702:980:25e0::/64
IPv6 Delegated Prefix Subnet (including length) 2600:1702:980:25ef::/64
IPv6 Delegated Prefix: 
2600:1702:980:25ef/64
Start Range:  2600:1702:980:25ef:0:0:0:0
End Range:  2600:1702:980:25ef:ffff:ffff:ffff:ffff
No. of host:  18446744073709551616
Subnet this into 16 networks
2^4 = 16 
You take the power of 3 and add it to 64 
/64 + 4 = /68

You take the block to the left of 25ef 
You create an interesting mask 1111b nibble

8 4 2 1 16 constant 
1 1 1 1 = 15 mask nibble

subtract them 
16 constant 
- 15 mask nibble 
1 interesting nibble
The red numbers are what get changed with the interesting nibbles.
2600 1702 980 25ef 0000 /68 
2600 1702 980 25ef 1000 /68 
2600 1702 980 25ef 2000 /68 
2600 1702 980 25ef 3000 /68 
2600 1702 980 25ef 4000 /68 
2600 1702 980 25ef 5000 /68 
2600 1702 980 25ef 6000 /68 
2600 1702 980 25ef 7000 /68
2600 1702 980 25ef 8000 /68 
2600 1702 980 25ef 9000 /68 
2600 1702 980 25ef A000 /68 
2600 1702 980 25ef B000 /68 
2600 1702 980 25ef C000 /68 
2600 1702 980 25ef D000 /68 
2600 1702 980 25ef E000 /68 
2600 1702 980 25ef F000 /68
Here is the first subnet range
2600 1702 980 25ef 0000 0000 0000 0000 to 2600 1702 980 25ef 0FFF FFFF FFFF FFFF

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