Head to head
Claude Opus 5.5 vs Claude Fable 5.1
Claude Opus 5.5 from Anthropic against Claude Fable 5.1 from Anthropic — specification, price and every benchmark both makers have published, in one table.
At a glance
Benchmarks
Claude Opus 5.5 leads
Claude Opus 5.5 wins 1 of the 1 benchmarks both models report, Claude Fable 5.1 wins 0, by a wide margin. The average gap across shared tests is 10.6 points.
Price
Claude Opus 5.5 is cheaper
On a 3:1 input-to-output mix, Claude Opus 5.5 costs $8.00 per million tokens against $20.00 for Claude Fable 5.1 — about 2.5× less. Remember that a reasoning model bills its thinking as output, so cost per answer can diverge much further than cost per token.
What actually differs
- These two are closely matched on the specification side — same broad capabilities, same licensing posture. The decision comes down to the benchmark rows and the price.
Scorecard
Which is better at what
Maths, coding, reasoning and the rest — one line each, averaged over the benchmarks both models actually report.
| Category | Claude Opus 5.5 | Claude Fable 5.1 | Better at this |
|---|---|---|---|
| ReasoningNeither model reports this | — | — | Not comparable |
| MathsNeither model reports this | — | — | Not comparable |
| CodingTerminal-Bench 4.0 | 66.4% | 55.8% | Claude Opus 5.5+10.6 |
| KnowledgeNeither model reports this | — | — | Not comparable |
| MultimodalNeither model reports this | — | — | Not comparable |
| Instruction followingNeither model reports this | — | — | Not comparable |
| Human preferenceNeither model reports this | — | — | Not comparable |
| Categories wonOut of 1 comparable | 1 | 0 | Claude Opus 5.5 |
Each category averages only the benchmarks every model here reports, so no one is credited for a test the other did not run. A category with no shared test is marked Not comparable rather than guessed at.
Side by side
Claude Opus 5.5 and Claude Fable 5.1, row by row
| Attribute | Claude Opus 5.5Anthropic | Claude Fable 5.1Anthropic |
|---|---|---|
| Specification | ||
| MakerWho built it | Anthropic | Anthropic |
| Released | 2026-09 | 2026-09 |
| Context windowHow much can go in at once | 1,000,000 tokens | 1,000,000 tokens |
| Max output | 128,000 tokens | 128,000 tokens |
| Input | Text, Image | Text, Image |
| ReasoningSpends extra tokens thinking before it answers | Yes | Yes |
| Tool calling | Yes | Yes |
| Knowledge cutoff | 2026-06 | 2026-06 |
| Licence | Proprietary | Proprietary |
| Open weightsCan you download and run it yourself | No | No |
| Price | ||
| Input priceUSD per million tokens in | $4.00 | $10.00 |
| Output priceUSD per million tokens out | $20.00 | $50.00 |
| Cached input | $0.20 | $0.25 |
| Blended 3:1A 3-in-to-1-out million-token mix — a fairer single number than input price alone | $8.00Cheapest | $20.00 |
| Published benchmarks | ||
| SWE-bench ProA harder, contamination-resistant successor to SWE-bench Verified, drawn from commercial and copyleft repositories that were never public training data. | Not reported | |
| Terminal-Bench 4.0End-to-end tasks in a real terminal — install, build, debug, run — scored on whether the machine ends up in the required state. | ||
| Links | Full page | Full page |
| Row verified | 2026-10 | 2026-09 |
Where these numbers come from
Every score on this page is a published figure, taken from the model's own card, system card, technical report or release post, or from a public leaderboard. CorX Labs did not run these evaluations. Most are self-reported by the lab that built the model, which means they were produced under that lab's own choice of prompt, scaffold and number of attempts — so treat them as a starting point for a shortlist, not as a settled ranking.
A score someone other than the model's maker measured is marked Independent and names its measurer. Those are the stronger numbers on this page — an outside harness has no reason to flatter anyone — and there are not many of them.
Where a figure has not been published, the cell reads Not reported rather than an estimate. Nothing here is inferred, interpolated or guessed. Each model records the month its row was last checked. Full method and caveats.
Questions
Claude Opus 5.5 or Claude Fable 5.1?
Is Claude Opus 5.5 better than Claude Fable 5.1?
Claude Opus 5.5 wins 1 of the 1 benchmarks both models report, Claude Fable 5.1 wins 0, by a wide margin. The average gap across shared tests is 10.6 points.
Which is cheaper, Claude Opus 5.5 or Claude Fable 5.1?
On a 3:1 input-to-output mix, Claude Opus 5.5 costs $8.00 per million tokens against $20.00 for Claude Fable 5.1 — about 2.5× less. Remember that a reasoning model bills its thinking as output, so cost per answer can diverge much further than cost per token.
What is the difference between Claude Opus 5.5 and Claude Fable 5.1?
These two are closely matched on the specification side — same broad capabilities, same licensing posture. The decision comes down to the benchmark rows and the price.
Related
