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.

One of the best parts of our newest Claude models is how they respond to effort without breaking the prompt cache in Claude Code, but I’ve received a lot of questions on this from users. What is

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.

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.

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

Tuning prompt caching, instructions, and effort can reduce Claude's cost without sacrificing application performance. Performance and cost are often viewed as a trade-off: to spend less, you accept

I’ve written previously about how to best prompt the newest generation of Claude 5 models and work with them iteratively to discover what you want to build. But when you send a message to Claude, the

Code migrations, projects that port a production codebase to a new language, were multi-year endeavors until recently. In the last month, individual developers at Anthropic migrated 10 code packages