Principles for designing evals and hillclimbing against them without fooling yourself, and how the claude-api skill's build-eval and hillclimb commands put them to work.

Introducing Claude Sonnet 5.5, the second model in the Claude 5.5 family. It’s a clear upgrade over Sonnet 5, runs more than 30% faster, and costs up to 30% less for most work.

Submit plugins to the Claude directory through a new directory submission portal. Package MCP connectors and Agent Skills, track your plugin through review, and see how it's used and found once it's live

The same token price can cost very different amounts per task. Learn what Claude Code tasks cost on Opus 5.5 and which settings change the bill.

Claude gives us N=4 super Yang-Mills to nine loops

How Claude Fable and Claude Opus models return classifier refusals and how to retry refused requests on a fallback model.

A rare Ebola strain is spreading in the DRC, with no confirmed vaccine. Global health organizations are using Claude to respond as fast as possible.

Inside our performance sprint: the benchmarks Claude built, the loop each Slack thread ran, and the guardrails that let us ship 3,000 changes safely.

Anthropic is an AI safety and research company that's working to build reliable, interpretable, and steerable AI systems.

How to prompt Opus 5.5, steer a long run, and check your results in Claude apps and Claude Code.

We’re partnering with Accenture on independent evaluation of frontier AI—part of our recent commitment to embed evaluators at Anthropic. Both we and Accenture expect to invest at least $1 billion to build capacity in this area over the next five years.

Today, the world can’t see what’s going on inside AI labs. Anthropic is proposing new metrics that would give the public visibility into frontier AI development.

Anthropic is an AI safety and research company that's working to build reliable, interpretable, and steerable AI systems.

Case studies from threat actors disrupted between December 2025 and August 2026 across seven areas of harm, from cyber operations to biological misuse.

We present an alignment assessment of four incidents in which Claude models gained unauthorized access to real third-party systems.

The Anthropic Economics Team models the effects of AI on the economy of 2030.