Claude Opus 5 vs Claude Sonnet 5.5
Different efforts: medium · high · 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
Opus 534.3
Sonnet 5.543.9
DeepSWE 1.1 DeepSWE 1.1: Agents change repository code to resolve software engineering tasks under the stated DeepSWE edition
Opus 568.9
Sonnet 5.5 · max70.5
WebDev Arena WebDev Arena: Human pairwise preferences in the stated webdev vote pool
Opus 5 · max1,689
Sonnet 5.51,710
SWE-bench Pro (v2 full) SWE-bench Pro (v2 full): Agents resolve repository issues under the network-locked v2 protocol; full and 51-task Hard results are separate
Opus 5 · xhigh99.4
Sonnet 5.5 · xhigh95.8
SWE-bench Pro (v2 hard) SWE-bench Pro (v2 hard): Agents resolve repository issues under the network-locked v2 protocol; full and 51-task Hard results are separate
Opus 5 · xhigh98
Sonnet 5.5 · xhigh70.6
SciCode SciCode: Writing code for real scientific computing problems (physics, biology, math)
Opus 551.5
Sonnet 5.553.7
Terminal-Bench Science 0.1 Terminal-Bench Science 0.1: Agents complete expert-authored research workflows across five scientific domains in a terminal
Opus 5 · max28.6
Sonnet 5.534.3
FrontierCode 1.1 FrontierCode 1.1: Agents implement changes in real repositories, graded against maintainer-defined requirements
Opus 5—
Sonnet 5.544.3
| Benchmark | Opus 5 | Sonnet 5.5 |
|---|---|---|
| Terminal-Bench 4.0 | 34.3 | 43.9 |
| DeepSWE 1.1 | 68.9 | 70.5 · max |
| WebDev Arena | 1,689 · max | 1,710 |
| SWE-bench Pro (v2 full) | 99.4 · xhigh | 95.8 · xhigh |
| SWE-bench Pro (v2 hard) | 98 · xhigh | 70.6 · xhigh |
| SciCode | 51.5 | 53.7 |
| Terminal-Bench Science 0.1 | 28.6 · max | 34.3 |
| FrontierCode 1.1 | — | 44.3 |
Specs
| Spec | Opus 5 | Sonnet 5.5 |
|---|---|---|
| Input, per 1M | $5 | $2 |
| Output, per 1M | $25 | $10 |
| Cost per task? | $2.19 | $0.88 |
| Speed, tok/s | 55 | 106 |
| 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 → Sonnet 5.5
No forced tool use›
Forced tool_choice any or tool returns HTTP 400; remove the forced choice.
Replace disabled thinking›
Disabled thinking returns HTTP 400; use between_tools for the lowest thinking setting.
No manual thinking budgets›
Manual thinking budgets and extra between_tools fields return HTTP 400; remove manual budgets and send between_tools without display, budget_tokens or block_binding.
Remove sampling parameters›
Non-default temperature, top_p or top_k returns HTTP 400; remove these parameters.
No assistant prefill›
A prefilled final assistant turn returns HTTP 400; remove that prefill.
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.
Sonnet 5.5 → Opus 5
Nothing known.