API/accountId: there seem to be 2 kinds of formats for accountId. difference?

Question

I just started using the API, and i noticed that the accountId looks a bit different between people.

For some people it looks like: 5d5bd05c3aeeabc123abc123

For other: 123456:4ac97bc8-ab12-ab12-8d38-eda562abc123

The second format looks newer, more modern:) It seems to have an identifier for our domain and uses an uuid.

Its about 50/50 (a bit more with the modern version).

Why are there 2 kinds? What decides this?
It doesnt seem to be as simple as "the newest users have the modern version".

Heinrich Ulbricht (WikiTraccs) · Answer

I'm wondering the same, is there any new information regarding the account ID formats?

My impression at some point was that the 123456:4ac97bc8-ab12-ab12-8d38-eda562abc123 format is used for accounts that stem from on-prem to cloud migrations  (so, accounts with a "history") and 5d5bd05c3aeeabc123abc123 is the format for newly created cloud accounts.

Prince Nyeche - ELFAPP · Answer

Hi @Alexander Kolodziej

AccountId is auto generated and it's random, so whenever a new user is created, i.e. never had an Atlassian account before. Atlassian systems will automatically generate the accountId. Now when that happens it can select the format from either pool.

* 5d5bd05c3aeeabc123abc123
* 123456:4ac97bc8-ab12-ab12-8d38-eda562abc123

Any that falls into either line gets chosen as the accountId and assigned to the user's email to be used across Atlassian Suite. I believe the reason behind it could most probably be due to "security" and how each alphanumeric string translate to that security. however this is just speculation.