Claude Opus 5.5 vs GPT-6 Astra
| Benchmark | Opus 5.5 | GPT-6 Astra |
|---|---|---|
| Terminal-Bench 4.0 | 52.5 | 49.5 |
| DeepSWE 1.1 | 72.3 · max | 72.8 |
| FrontierCode 1.1 | 57.1 | 47 · max |
| WebDev Arena | 1,807 · max | 1,774 · max |
| SciCode | 59.3 | 54.2 |
| Terminal-Bench Science 0.1 | 43.3 | 63.3 · max |
| MirrorCode | 77.4 · max | 46.7 · high |
| SWE-bench Pro (v2 full) | — | 96.9 · high |
| SWE-bench Pro (v2 hard) | — | 90.2 · high |
| MultiLangBenchlab | — | 87.4 |
Specs
| Spec | Opus 5.5 | GPT-6 Astra |
|---|---|---|
| Input, per 1M | $4 | $10 |
| Output, per 1M | $20 | $50 |
| Cost per task? | $1.34 | $1.54 |
| Speed, tok/s | 81 | 59 |
| Context | 1M | 1.05M |
| Weights | Closed | Closed |
| Released | Sep 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
Monitoring can return HTTP 403›
Misalignment monitoring can return HTTP 403 before streaming or errors after output; match misalignment_policy_violation and handle stream errors.
No none reasoning effort›
The none reasoning effort is unsupported on GPT-6 Astra and GPT-6.1 Sol; use low instead.
Remove unsupported sampling parameters›
When reasoning effort is not none, remove temperature, top_p and top_logprobs, plus Chat Completions logprobs or Responses output logprobs inclusion.
Context: 1.05M → 1M
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.