It looks like tech.instacart.com is hosted on Medium. The redirect is part of the auth flow. If you have a Medium account, you would have logged in to medium.co

It looks like tech.instacart.com is hosted on Medium. The redirect is part of the auth flow. If you have a Medium account, you would have logged in to medium.com, not tech.instacart.com. If you don't have a Medium account, Medium still will want to add first-party tracking information to your interaction with tech.instacart.com and all other Medium properties. So this client-side redirect flow enables them to capture that association. This is presumably what the `gi=85c0588ca374` query parameter is in the follow-on redirect. I would guess that `gi` stands for "global identity" or something.