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According to the
privacy notice, the retention is a bit longer unless one has activated "limited retention" in his profile. For ease of view though, I’ll quote the relevant part of the notice:
IP-address retention
IP address retention works in this way:
Thing Normal retention Limited retention Retention for guests
Full IP 6 months 3 months A few weeks
Partial IP 2 years N/A N/A
City geolocation 6 years 3 months N/A
You can opt into limited retention in your account settings. This will apply only to logs created after you change the setting, and doing so will make it much more difficult for you to recover your account if it is ever lost.
Between 6 and 24 months, the IP linearly loses least-significant bits over time. For example, the IP 123.234.210.221 would lose 8 bits and become the prefix 123.234.210.0/24 approximately 10.5 months after it was logged. For IPv6, the least-significant 66 bits are dropped after 6 months, and then the remaining bits are dropped linearly over the 1.5-year period.
The city geolocation locates you to the nearest large city according to your IP address.
Exception: if you click on a "ping link" as part of a manual account recovery process, the IP log created by this action has possibly-indefinite retention.
Of course there are likely to be backups and such that make snapshot data persist as a backup.