Google's Gary Illyes said that the Googlebot JSON file IP address list is updated within a few days of a new IP being added to the list of IPs that Googlebot crawls from. "We got a few comments about whether the list is up-to-date; the answer was always yes, within a margin of a few days," Gary said.
Gary said this on LinkedIn where he explained why it is a few days. "The few days margin comes from the exporter running only once a week, because the list changes very rarely. The exporter still runs automatically once a week, but now it updates the creation time field with the new time and publishes the list even if it's unchanged. This is a no-op change for tools that consume the list, but hopefully prevents comments about whether the list is up-to-date," Gary explained.
Gary also added that "We changed the googlebot.json exporter to publish the list of Googlebot IP ranges and update the creation time even if there were no changes in the list."
I should note, the JSON file was indeed updated a week or so ago, with not just some formatting changes but also Google added {"ipv4Prefix": "34.22.85.0/27"},
Forum discussion at LinkedIn.
Image credit to @okaylizzi
