Introducing Claude Opus 5.5

Introducing Claude Opus 5

Opus 5 is a step change improvement for the Opus tier powering long-running agents while delivering improvements in coding and professional work.

Claude Opus 5: The System Card

Claude Opus 5 is trying to be the best of both worlds.

Prompting Claude Opus 5

Behavioral differences and prompting patterns for Claude Opus 5, covering response verbosity, agentic narration, task scoping, subagent delegation, self-correction, and output artifacts when thinking is disabled.

Claude Opus 4.8: The System Card

Only six weeks after Opus 4.7, we have Opus 4.8.

Introducing Claude Opus 4.6

Anthropic Readies Opus 4.7 and Design Tool as VCs Offer $800 Billion Valuation

Anthropic is preparing to release Claude Opus 4.7 and a natural language design tool as early as this week, while venture capital firms have offered to invest at valuations exceeding $800 billion – more than double the company’s last official price tag.The model ID anthropic-claude-opus-4-7 appeared on Google Vertex AI’s quota management page for EU […]

Claude Opus 5 Is Highly Capable, But Is No Mythos

Claude Opus 5 is a weirder than usual release to evaluate, for two reasons.

Opus 4.7 isn't dumb, it's just lazy — Shimin Zhang

Some follow up experiments with Claude Opus 4.7 based on Simon Willison's Pelican Benchmark Shocker.

Claude Code, Codex and Agentic Coding #8

When I started this series, everyone was going crazy for coding agents.

ᖴά𝐂τσ on Twitter / X

Unpopular opinion: Opus 4.7 isn't the problem. The problem is a $200/mo "Max" plan that burns out in 15 minutes of real coding. Anthropic shipped a model people want to use and a pricing tier that punishes them for using it. That's not a rate limit. That's a strategy. pic.twitter.com/DVbzvdUHdq— ᖴά𝐂τσ (@cryptofacto) April 17, 2026

Prompting Claude Opus 5.5

Behavioral differences from Claude Opus 5 and the prompting and harness patterns that address them: effort calibration, thinking behavior in API integrations and chat, progress updates, unattended and multiagent tasks, safeguard refusals, frontend design, complex visual inputs, multi-app workflows, and pasted text in user messages.