Can't find it in buildbucket either:

https://apis-explorer.appspot.com/apis-explorer/?base=https://cr-buildbucket.appspot.com/_ah/api#p/buildbucket/v1/buildbucket.get?id=8951530866804323000&_h=1&

That being said, this should've returned 404, not 500

Interesting! I've actually tried to enter 8951529651644382896, but as soon as I hit Shift-Enter on the input field of the RPC explorer, it changes the ID to 8951529651644383000. Are we using floats for these numbers? :-/

Aha! You found the maximum size for a javascript number.

We work around that by putting quotes around the number :/

https://luci-milo.appspot.com/rpcexplorer/services/milo.BuildInfo/Get?request={%20%20%20%20%22buildbucket%22:%20{%20%20%20%20%20%20%20%20%22id%22:%20%228951529651644382896%22%20%20%20%20}}

Hm. Would never have guess that :-).

WAI?

This is not WAI because Milo should return 404, not 500.