Harness design for long-running application development
…Running the harness For the first version of this harness, I used Claude Opus 4.5, running user prompts against both the full harness and a single-agent system for comparison. I…
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What’s next?
Users will find Opus 4.8 to be a modest but tangible improvement on its predecessor. There’s still more to be done: we’re working on developing and releasing models that provide many of the same capabilities as Opus at a lower cost. Not only that, but we plan to release a new class of model with even higher intelligence than Opus. As part of Project Glasswing, a small number of organizations are currently using Claude Mythos Preview for cybersecurity work. Models of this capability level require stronger cyber safeguards before they can be generally released. We’re making swift progress on dev
Introducing Claude Opus 4.8Top stories
Project Glasswing: An initial update
…In the three weeks since launch, Claude Opus 4.7 has been used to patch over 2,100 vulnerabilities. (This is faster than the open-source patching described above in large part…
LLMs and biorisk
…Participants with access to Claude 4 models—especially Claude Opus 4—received much higher scores and developed plans with substantially fewer critical failures compared to the internet-only control group. Text-based…
AI agents find smart contract exploits
…Balancer Added a Related Work section Updated the Acknowledgments section Edited December 8, 2025: Modified text to reflect accurate knowledge cutoff date for Claude Opus 4.5 Appendix Our benchmark Our dataset…
Next-generation Constitutional Classifiers: More efficient protection against universal jailbreaks
…In total, it adds roughly 1% compute overhead if applied to Claude Opus 4.0 traffic. It’s also substantially more robust. We conducted over 1,700 cumulative hours of red-teaming…
Introducing advanced tool use on the Claude Developer Platform
…4 } }, { "title": "Add dark mode support", "labels": ["feature-request", "ui"], "reporter": { "id": "USR-67890", "name": "Alex Chen" } }, { "title": "Update API documentation" } ] } From these three examples, Claude learns: Format conventions : Dates use YYYY…
Long-running Claude for scientific computing
…Crucially, Claude can edit these instructions as it works, updating them for future work as it works through issues. Here is an early CLAUDE.md for the cosmological Boltzmann solver project, showing…
Measuring AI agent autonomy in practice
…One of the most widely cited capability assessments is METR’s “Measuring AI Ability to Complete Long Tasks,” which estimates that Claude Opus 4.5 can complete tasks with a 50% success…
Coding agents in the social sciences
…Our survey came around two months after a flurry of discussion about Claude Code and Opus 4.6 that kicked off in late December of 2025. Yet even among interested respondents who…
Assessing Claude Mythos Preview’s cybersecurity capabilities
…Use generally available frontier models to strengthen defenses now . Current frontier models, like Claude Opus 4.6 (and those of other companies), remain extremely competent at finding vulnerabilities , even if they are…