Claude Opus 5.5 vs Fable 5.1: $4 vs $10 per million input tokens

Claude Opus 5.5 vs Fable 5.1 is mostly a question of price against ceiling. Opus 5.5 costs $4 per million input tokens and $20 per million output tokens, 60% less than Fable 5.1 at $10 and $50. Anthropic's docs say to start with Opus 5.5 and move to Fable 5.1 only when your own tests still fall short. This comparison is based on the products' docs and published results, not our own testing, and the prices are as of November 2, 2026.

Anthropic's models overview recommends Opus 5.5 for most workloads and Fable 5.1 for demanding reasoning and long-horizon agentic work. For the Opus 5.5 against Sonnet 5.5 choice, see our Opus 5.5 vs Sonnet 5.5 comparison.

Specs and prices side by side

Sources: Anthropic's models overview, the Opus 5.5 and Fable 5.1 model pages, and the pricing page. Batch requests are 50% off on both. Anthropic says the latency row is relative to the current lineup and that real speed depends on prompt length, output length and effort.

The specs match on everything except price, speed and default effort. Both read 1M tokens, write up to 128K, and share the same cutoff. So the choice is not about what fits in a prompt.

What Anthropic's benchmarks show

Anthropic's Opus 5.5 announcement says the model performs at the level of Fable 5.1 on most work. On its published table, Opus 5.5 scores higher than Fable 5.1 on every row listed:

These are Anthropic's own numbers. Unless noted, Opus 5.5 ran with adaptive thinking at max effort. Terminal-Bench 4.0 used xhigh effort for Opus 5.5, with a standard error of 2.6 points. Anthropic also says the gap between the two in its own use is narrower than the scores suggest. Several rows are within a point or two, which is inside the noise on benchmarks like these.

Anthropic notes that production safeguards were on, and that when they stepped in, older models finished some tasks. It says this likely lowers Opus 5.5's scores. We found no independent test that compares the two models directly.

When Fable 5.1 is still the pick

Anthropic's guide to choosing a model lists Fable 5.1 as the answer when you need the highest available capability: agent sessions that run for hours, multistep deep research, and analysis carried through to a finished document, spreadsheet or deck. Its advice is to test Opus 5.5 first, at xhigh or max effort, and move up only if your evals still fall short.

Fable 5.1 shares its capabilities with Claude Mythos 5.1, which Anthropic limits to organizations verified through programs such as its Cyber Verification Program. Our Claude Fable explainer covers how the two relate. The Fable docs also describe handling classifier refusals and retrying on another Claude model, which is worth planning for if you build on it.

What each costs on claude.ai

Per Anthropic's pricing page on November 2, 2026:

For a person on Pro, Opus 5.5 is the model you can use without extra spend. Fable starts on Max.

Which one to use

Use Opus 5.5 by default. It is cheaper by 60%, faster per Anthropic's own rating, and ahead on Anthropic's published benchmarks. Use Fable 5.1 for the hardest long-running agent and research jobs, and only after your own tests show Opus 5.5 falls short. If your job is simple and high-volume, neither is the cheapest option; Sonnet 5.5 costs $2 and $10.

Watch for independent evaluations of the pair. Until they appear, the only head-to-head numbers come from Anthropic.