Claude Sonnet 5.5 vs GPT-6 Astra
| Benchmark | Sonnet 5.5 | GPT-6 Astra |
|---|---|---|
| Arena Text · creative writing | 1,465 · xhigh | 1,450 · max |
| Harvey LAB-AA 1.1 | 2.8 · max | 8.6 · max |
| EQ-Bench Longform Creative Writing 1.11 | — | 82.8 |
| EQ-Bench Creative Writing v3 | — | 2,173.3 |
| Lech Mazur Short-Story | — | 3.4 · high |
Specs
| Spec | Sonnet 5.5 | GPT-6 Astra |
|---|---|---|
| Input, per 1M | $2 | $10 |
| Output, per 1M | $10 | $50 |
| Cost per task? | $0.88 | $1.54 |
| Speed, tok/s | 106 | 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.
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.