Claude Fable 5 vs Claude Opus 5.5
Different efforts: max · medium · Compare all at high
Terminal-Bench 4.0 Terminal-Bench 4.0 · source setting 2: Agents use a terminal to complete executable coding, system administration and research tasks in the 4.0 suite
Fable 542.4
Opus 5.552.5
DeepSWE 1.1 DeepSWE 1.1: Agents change repository code to resolve software engineering tasks under the stated DeepSWE edition
Fable 569.7
Opus 5.5 · max72.3
WebDev Arena WebDev Arena: Human pairwise preferences in the stated webdev vote pool
Fable 5 · high1,624
Opus 5.5 · max1,807
SciCode SciCode: Writing code for real scientific computing problems (physics, biology, math)
Fable 561
Opus 5.559.3
MirrorCode MirrorCode: Agents reimplement software projects by observing their behavior
Fable 5 · high63.9
Opus 5.5 · max77.4
FrontierCode 1.1 FrontierCode 1.1: Agents implement changes in real repositories, graded against maintainer-defined requirements
Fable 5—
Opus 5.557.1
Terminal-Bench Science 0.1 Terminal-Bench Science 0.1: Agents complete expert-authored research workflows across five scientific domains in a terminal
Fable 5—
Opus 5.543.3
Terminal-Bench Hard (version unstated) Terminal-Bench Hard (version unstated): Agents solve difficult software, system-administration and data-processing tasks in a terminal
Fable 562.9
Opus 5.5—
| Benchmark | Fable 5 | Opus 5.5 |
|---|---|---|
| Terminal-Bench 4.0 | 42.4 | 52.5 |
| DeepSWE 1.1 | 69.7 | 72.3 · max |
| WebDev Arena | 1,624 · high | 1,807 · max |
| SciCode | 61 | 59.3 |
| MirrorCode | 63.9 · high | 77.4 · max |
| FrontierCode 1.1 | — | 57.1 |
| Terminal-Bench Science 0.1 | — | 43.3 |
| Terminal-Bench Hard (version unstated) | 62.9 | — |
Specs
| Spec | Fable 5 | Opus 5.5 |
|---|---|---|
| Input, per 1M | $10 | $4 |
| Output, per 1M | $50 | $20 |
| Cost per task? | $8.75 | $1.34 |
| Speed, tok/s | 67 | 81 |
| Context | 1M | 1M |
| Weights | Closed | Closed |
| Released | Jun 2026 | Sep 2026 |
| See images | ✓ | ✓ |
| Read PDFs | Partial | ✓ |
| Hear audio | — | — |
| Watch video | — | — |
| Call tools | ✓ | ✓ |
| Force a tool call | Partial | — |
| Return strict JSON | ✓ | ✓ |
| Search the web | ? | ✓ |
| Run code | ? | ✓ |
| Use a computer | ? | ✓ |
What breaks when you switch
Fable 5 → Opus 5.5
No forced tool use›
Forced tool_choice any or tool returns HTTP 400; remove the forced choice.
Thinking is always on›
Disabled thinking or a manual budget returns HTTP 400; omit thinking or use adaptive thinking.
Remove sampling parameters›
Non-default temperature, top_p or top_k returns HTTP 400; omit these parameters and use prompting.
No assistant prefill›
Assistant prefill returns HTTP 400; use structured outputs or system instructions, with system instructions on Bedrock.
Old computer tool rejected · Claude API / Google Cloud›
The computer_20251124 tool returns HTTP 400 on the Claude API and Google Cloud; use computer_toolset_20260801 there.
Return thinking blocks unmodified›
Edited, reordered or partially dropped thinking blocks return HTTP 400; echo assistant messages complete and unmodified with tool results.
Opus 5.5 → Fable 5
Nothing known.