Claude Opus 5 Is Highly Capable, But Is No Mythos
Zvi (Don't Worry About the Vase) TheZvi ● Covered by 5 sources
Anthropic released Claude Opus 5, positioning it as a cheaper alternative to their flagship Fable 5 model at half the API token cost while delivering comparable performance on most real-world tasks. Opus 5 achieves state-of-the-art scores on benchmarks like Frontier-Bench and GDPval-AA, and is notably the most resistant to prompt injection attacks of any Claude model to date. However, the model struggles with high-level autonomous reasoning compared to Fable, has polarizing personality traits that many users find off-putting, and ultimately does not expand what's possible—it mainly offers a cost-effective option for specific use cases like subagent work and bounded tasks.
Why it matters
Claude Opus 5 is a weirder than usual release to evaluate, for two reasons. The most obvious is that Fable 5 already exists. Opus 5 is pitched not as the world’s most advanced AI model, but as a way to … Continue reading →
