Lingots not awarded
I practiced just now and hit day 440 in my streak, but I was not awarded 44 lingots for the multiples of 10 days - At least I don't see the message that I was. I didn't happen to look at my lingot count before I practiced so technically I am not sure if it was awarded or not. Any way to check?
Actually, this has been the case for almost a month now. Duolingo is currently running a test to see if removing the streak award will have any negative impacts. Did you receive lingots when you got 430 days? If yes, I guess they may have now increased the percentage of users for whom the award is removed.
Double or Nothing is still unchanged. I guess they just wanted to reduce ways of earning lingots, not altogether remove it. They removed the easiest method first (earning lingots for flawless completion of any lesson) and now the streak based method. For new users, they will now have just enough to buy the bonus options and give a few here and there for helpful comments; they will not be brimming with them :)
An A/B test is when a change is tested for effects. One half of people (say group A) get to see the change, while the other (say group B) don't. The performance of the two groups is then looked at in light of the change and a decision is made as to whether or not to introduce the change through out.
As others have said, it's an A/B test they are running. IMO its the worst. People criticized me before for "caring about lingots too much". Well, tbh, there is zero incentive to log in every single day and make it a habit if there is no reward for doing so. Personally, I think this test should have been done with new users and compared their results to the existing userbase, not dragging all of us into it.