Online learning algorithms continually update their models as data arrive, making it essential to accurately estimate the expected loss at the current time step. The prequential method is an effective estimation approach which can be practically deployed in various ways. However, theoretical guarantees have previously been established under strong conditions on the algorithm, and practical algorithms have hyperparameters which require careful tuning. We introduce OEUVRE, an estimator that evaluates each incoming sample on the function learned at the current and previous time steps, recursively updating the loss estimate in constant time and memory. We use algorithmic stability, a property satisfied by many popular online learners, for optimal updates and prove consistency, convergence rates, and concentration bounds for our estimator. We design a method to adap-tively tune OEUVRE's hyperparameters and test it across diverse online and stochastic tasks. We observe that OEUVRE matches or outperforms other estimators even when their hyperparameters are tuned with oracle access to ground truth.

Last week, to formally consecrate the beginning of the holiday season, my fiancée threw on Christmas With the Kranks. The wretched 2004 Tim Allen film notched an impressively bad 5 percent on Rotten Tomatoes, with most critics complaining about the screenplay's awkward marriage of lifeless Middle American sentimentality with the sort of visual gags you might find in Progressive commercials. Christmas With the Kranks is not making the Criterion Collection anytime soon, and I think it's fair to say that there are better ways to spend a winter evening, but if you value the season like we do--and intend to have a Christmas movie on-screen at all times until New Year's--then you must ration the heavy hitters of the genre for the premium slots on the calendar. Or, in other words, if you want to watch Home Alone on Dec. 22, then you might be forced to spend a night with Tim Allen on Dec. 5. We all know what the classics are. The Mount Rushmore of Christmas movies, at least according to mainstream millennial opinion, are Elf, A Charlie Brown Christmas, the Chuck Jones–animated How the Grinch Stole Christmas, and the aforementioned Home Alone.