Claude Opus 5.5 vs Claude Sonnet 5.5

Claude Opus 5.5
$1.34 / task
Wins 6 of 9 benchmarks
Claude Sonnet 5.5
$0.88 / task
Wins 0 of 9 benchmarks
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 5.552.5
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 5.5 · max72.3
Sonnet 5.5 · max70.5
FrontierCode 1.1 FrontierCode 1.1: Agents implement changes in real repositories, graded against maintainer-defined requirements
Opus 5.557.1
Sonnet 5.544.3
WebDev Arena WebDev Arena: Human pairwise preferences in the stated webdev vote pool
Opus 5.5 · max1,807
Sonnet 5.51,710
SciCode SciCode: Writing code for real scientific computing problems (physics, biology, math)
Opus 5.559.3
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 5.543.3
Sonnet 5.534.3
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 5.5—
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 5.5—
Sonnet 5.5 · xhigh70.6
MirrorCode MirrorCode: Agents reimplement software projects by observing their behavior
Opus 5.5 · max77.4
Sonnet 5.5—

Specs

SpecOpus 5.5Sonnet 5.5
Input, per 1M$4$2
Output, per 1M$20$10
Cost per task?$1.34$0.88
Speed, tok/s81106
Context1M1M
WeightsClosedClosed
ReleasedSep 2026Sep 2026
See images✓✓
Read PDFs✓✓
Hear audio——
Watch video——
Call tools✓✓
Force a tool call——
Return strict JSON✓✓
Search the web✓✓
Run code✓✓
Use a computer✓✓

What breaks when you switch

Opus 5.5 → 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 5.5
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.