Claude Opus 5 vs Claude Opus 5.5
Harvey LAB-AA 1.1?
Opus 5—
Opus 5.5at max4.2
| Benchmark | Opus 5 | Opus 5.5 |
|---|---|---|
| Arena Text · creative writing | 1,471 · max | 1,519 · high |
| EQ-Bench Longform Creative Writing 1.11 | 86.3 | 84.6 |
| EQ-Bench Creative Writing v3 | 2,133.5 | 2,050.8 |
| Lech Mazur Short-Story | 3.7 · xhigh | 3.7 · high |
| Harvey LAB-AA 1.1 | — | 4.2 · max |
Specs
| Spec | Opus 5 | Opus 5.5 |
|---|---|---|
| Input, per 1M | $5 | $4 |
| Output, per 1M | $25 | $20 |
| Cost per task? | $2.19 | $1.34 |
| Speed, tok/s | 51 | 82 |
| Context | 1M | 1M |
| Weights | Closed | Closed |
| Released | Jul 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
Opus 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 → Opus 5
Nothing known.