Large language models (LLMs) are increasingly deployed as agents in dynamic, real-world environments, where success requires both reasoning and effective tool use. A central challenge for agentic tasks is the growing context length, as agents must accumulate long histories of actions and observations. This expansion raises costs and reduces efficiency in long-horizon tasks, yet prior work on context compression has mostly focused on single-step tasks or narrow applications. We introduce Agent Context Optimization (ACON), a unified framework that optimally compresses both environment observations and interaction histories into concise yet informative condensations. ACON leverages compression guideline optimization in natural language space: given paired trajectories where full context succeeds but compressed context fails, capable LLMs analyze the causes of failure, and the compression guideline is updated accordingly. Furthermore, we propose distilling the optimized LLM compressor into smaller models to reduce the overhead of the additional module. Experiments on AppWorld, OfficeBench, and Multi-objective QA show that ACON reduces memory usage by 26-54% (peak tokens) while largely preserving task performance, preserves over 95% of accuracy when distilled into smaller compressors, and enhances smaller LMs as long-horizon agents with up to 46% performance improvement. Our code is available at https://github.com/microsoft/acon.

Random Utility Models (RUMs) are a classical framework for modeling user preferences and play a key role in reward modeling for Reinforcement Learning from Human Feedback (RLHF). However, a crucial shortcoming of many of these techniques is the Independence of Irrelevant Alternatives (IIA) assumption, which collapses \emph{all} human preferences to a universal underlying utility function, yielding a coarse approximation of the range of human preferences. On the other hand, statistical and computational guarantees for models avoiding this assumption are scarce. In this paper, we investigate the statistical and computational challenges of learning a \emph{correlated} probit model, a fundamental RUM that avoids the IIA assumption. First, we establish that the classical data collection paradigm of pairwise preference data is \emph{fundamentally insufficient} to learn correlational information, explaining the lack of statistical and computational guarantees in this setting. Next, we demonstrate that \emph{best-of-three} preference data provably overcomes these shortcomings, and devise a statistically and computationally efficient estimator with near-optimal performance. These results highlight the benefits of higher-order preference data in learning correlated utilities, allowing for more fine-grained modeling of human preferences. Finally, we validate these theoretical guarantees on several real-world datasets, demonstrating improved personalization of human preferences.

A new survey from the Center for Democracy and Technology reveals nearly 20% of U.S. high school students use AI for romantic relationships.

Our great big world captured in beautiful detail. Breakthroughs, discoveries, and DIY tips sent every weekday. In 1839, photography as a medium was made widely available to the public. Named in honor of photography's milestone year, the 1839 Awards celebrates stunning imagery from around the world. This year's competition welcomed entries from 79 countries and awarded winners across professional and non-professional categories.

W hen the first ever stage adaptation of the global book and film franchise The Hunger Games opens its doors in London next week, fans paying up to £200 have been promised an "electrifying" and "immersive" experience. The show at the purpose-built 1,200 seat Troubadour in Canary Wharf, which features Hollywood A-lister John Malkovich appearing via screen as the evil President Snow who oversees the televised spectacle of teenagers fighting to the death, is the latest in an explosion of launches looking to cash in on a boom in consumer demand for experiential entertainment, often linked to bankable franchises. The boom in the market for experimental, unusual nights out and shows is well established, from escape rooms, axe throwing and slumber parties to Secret Cinema's Olympic Park takeover to recreate the setting for Back to the Future and the hugely successful Abba Voyage. Recent pop-ups include experiences linked to Minecraft, Jurassic World and Squid Game. As big money has rolled into the sector, so too has a desire from companies to rely on solid gold intellectual property to bring in the crowds - with mixed results.

Sign up to receive it in your inbox. In " Final Boy," your story in this week's issue, Rick is a writer of fan fiction about the eighties sitcom "Charles in Charge." How does Rick think of his writing, and how does it fit into his conception of himself? Rick is a guy who has always loved books and used to study creative writing. He's worked for decades in the gig economy, long before it was even called that, doing freelance copy editing and the like.

The watershed moment Trump changed course on Israel after Netanyahu shattered their once-unbreakable bond: 'We felt betrayed' Kim Kardashian stuns onlookers in horrifying MASKED look at one of Hollywood's biggest galas DAPHNE BARAK: How I delivered the final, fatal blow to Andrew's fast-sinking reputation... and why Palace is right to still be deeply concerned Doctors expose the truth about melatonin... as terrifying side effects soar Gavin Newsom melts down as Pentagon plans to fire artillery shells over California highway during'No Kings' protest Olivia Nuzzi's memoir will reveal juicy text messages with RFK Jr. KENNEDY: Here's the truth of weird drug-fueled orgies in Congress that Tucker Carlson is investigating... it makes me sick to my stomach JANA HOCKING: I've uncovered the ultimate new sex secret and had the best night of my life... no wonder more women are trying it Limp Bizkit bassist Sam Rivers dead at 48 as iconic band pays tribute to'once-in-a-lifetime' talent Insiders reveal dark web of power behind earthquake of'No Kings' protests exploding across America Five safe haven investments if the global economy goes into meltdown (and one under the radar fund to buy RIGHT NOW): As more and more experts warn of a devastating fall in share prices... Inside the King's cold phone call that saw Prince Andrew lose his dukedom and have to cancel Sarah Ferguson's 66th birthday party as Epstein scandal exploded '90s icon looks unrecognizable as she teases her most infamous TV scene in bucket hat during rare outing Antonio Banderas and Melanie Griffith's daughter Stella, 29, weds her childhood sweetheart in dreamy Spanish wedding as actor toasts the newlyweds Stephen A. Smith makes racially-charged double standard accusation against LeBron James amid feud The Duchess of Scandal... who is now plain old Sarah: Fergie's humiliating downfall as King makes moves to'protect' her daughters Green Bay Packers' game in jeopardy with team stranded at airport less than 24 hours before kickoff Selena Gomez makes FIRST red carpet appearance with husband Benny Blanco since wedding as their'perfect' honeymoon is revealed READ MORE: Is there a God? It's a question that has been asked since the beginning of time: does God really exist? Traditionally, science has been the counterargument for the existence of a divine creator. However, French mathematicians Olivier Bonnassies and Michel-Yves Bollore now say that science'has become God's ally'. In a new book, the duo have distilled insights from 62 Nobel Prize winners and more than 100 leading scientists to pinpoint the scientific discoveries that could prove God is real.

OpenAI patched the ShadowLeak attack in August 2025 after hackers exploited ChatGPT to exfiltrate Gmail data through invisible email prompts without user interaction.

An illustration of how AI manipulates and changes images. An illustration of how AI manipulates and changes images. Ask Google's AI video tool to create a film of a time-travelling doctor who flies around in a blue British phone booth and the result, unsurprisingly, resembles Doctor Who . And if you ask OpenAI's technology to do the same, a similar thing happens. What's wrong with that, you may think?

Federal regulators investigate Tesla's Full Self-Driving technology over safety concerns, including 14 crashes and 23 injuries from traffic violations.