> Somewhere in GitHub's codebase, there's an if-statement checking when a repository was created to decide which ID format to return.

I doubt it. That's the beauty of GraphQL — each object can store its ID however it wants, and the GraphQL layer encodes it in base64. Then when someone sends a request with a base64-encoded ID, there _might_ be an if-statement (or maybe it just does a lookup on the ID). If anything, the if-statement happens _after_ decoding the ID, not before encoding it.

There was never any if-statement that checked the time — before the migration, IDs were created only in the old format. After the migration, they were created in the new format.

> That repository ID (010:Repository2325298) had a clear structure: 010 is some type enum, followed by a colon, the word Repository, and then the database ID 2325298.

It's a classic length prefix. Repository has 10 chars, Tree has 4.

> GitHub's migration guide tells developers to treat the new IDs as opaque strings and treat them as references. However it was clear that there was some underlying structure to these IDs as we just saw with the bitmasking

Great, so now GitHub can't change the structure of their IDs without breaking this person's code. The lesson is that if you're designing an API and want an ID to be opaque you have to literally encrypt it. I find it really demoralizing as an API designer that I have to treat my API's consumers as adversaries who will knowingly and intentionally ignore guidance in the documentation like this.

I just want to point out that Opus 4.5 actually knows this trick and will write the code to decode the IDs if it is working with GitHub's API lol