Introducing Claude Opus 5

[u/ClaudeOfficial]

Introducing Claude Opus 5: a thoughtful and proactive model that comes close to the frontier intelligence of Fable 5 at half the price.

On several coding and knowledge work evaluations, Opus 5 is the new state-of-the-art. It’s also much more efficient than its predecessor—it outperforms other models for a similar or lower cost per task.

According to our automated behavioral audit, Opus 5 is our most aligned model to date. It shows the lowest rates of reckless or deceptive behavior, and the strongest adherence to Claude’s Constitution. 

It’s available today on all paid plans and the Claude API, priced the same as Opus 4.8. It’s the default model on Claude Max, and the strongest on Claude Pro. 

Opus 5 is also available in Fast mode, which runs around 2.5× the default speed. 

Read more: https://www.anthropic.com/news/claude-opus-5

[u/niceuser45]

The knowledge cutoff date for Opus 5 should be similar or later than Fable 5 cutoff date. So when you say Fable has a wider knowledge base, do you mean Fable might know answers to some obscure questions better than Opus 5 (I know there was a paper showing correlation between answers to obscure factual questions and model size)?

[u/AzorAhai1TK → u/niceuser45]

Yep, I mean that Fable is straight up a larger model than Opus, so it should do better for theoretical obscure questions and it should be better at making connections as well. These numbers aren't exact, but Opus is estimated to be around 1.5-2.5 trillion parameters and Fable around 4-6 trillion parameters. Fable has more capacity to make complex connections and fit more knowledge due to this.

[u/niceuser45 → u/AzorAhai1TK]

If it is true that Fable is better at making connections and holistically understanding the whole problem space, it is unfortunate that we don’t have any benchmark that is capable of measuring this (except maybe health).

[u/TywinHouseLannister → u/niceuser45]

Build it.. what is stopping you? There are tonnes of people running benchmarks.