This is mostly as a notepad entry for myself, but putting here in case anyone finds it useful.
Nanog discussion about the prefix length from 2011:
The question is - "how long is the IPv6 prefix that I can announce?".
Here are some links to help understand the answer to this question:
RIPE recommendations
Practical experiments from RIPE on prefix visibility:
Nanog discussion about the prefix length from 2011: