Claude Opus 5.5 vs Gemini 3.8 Flash
| Benchmark | Opus 5.5 | Gemini 3.8 Flash |
|---|---|---|
| Humanity's Last Exam | 54.7 | 42.1 |
| Terminal-Bench 4.0 | 52.5 | 19.7 |
| AutomationBench-AA | 61.2 | 60.9 |
| Arena Text · creative writing | 1,519 · high | 1,487 · high |
| MMMU-Pro (vision) | 85.7 | 84.2 |
Specs
| Spec | Opus 5.5 | Gemini 3.8 Flash |
|---|---|---|
| Input, per 1M | $4 | !$0.75 |
| Output, per 1M | $20 | !$3.75 |
| Cost per task? | $1.34 | $0.93 |
| Speed, tok/s | 81 | — |
| Context | 1M | 1M |
| Weights | Closed | Closed |
| Released | Sep 2026 | Sep 2026 |
| See images | ✓ | ✓ |
| Read PDFs | ✓ | ✓ |
| 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
Sampling parameters are ignored›
temperature, top_p and top_k are ignored now and will cause HTTP 400 in future generations; remove them from requests.
No minimal thinking level›
The minimal thinking level returns an error; avoid minimal.
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.