Claude Opus 5 is a weirder than usual release to evaluate, for two reasons.
Claude Opus 5: The System Card
Claude Opus 5 is trying to be the best of both worlds.
Opus 5 is a great model. It's not great enough.
Claude Fable 5 and Claude Mythos 5
Today we’re launching Claude Fable 5: a Mythos-class model that we’ve made safe for general use.
Introducing Claude Opus 5.5
Claude Opus 5.5 leads in agentic coding and knowledge work, and costs 40% less to run than Opus 5 on typical workloads.
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.
How good is Mythos?
Is Claude Mythos Preview a particularly big jump in AI capabilities?
Claude Opus 4.7 Is Here: Release Confirmed April 16, 2026
Claude Opus 4.7 shipped April 16, 2026. SWE-bench 87.6%, xhigh mode, /ultrareview, 2,576px vision. Read our full first-look review.
Introducing Claude Opus 4.6
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 Mythos 5.1 and Fable 5.1: Capabilities
This is the weirdest situation in which to write a capabilities review.
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 5.5 anthropic.com/claude-opus-5-5
