Claude Sonnet 5 vs GPT-5.6 Luna: which should you choose in 2026?
Claude Sonnet 5 (by Anthropic) and GPT-5.6 Luna (by OpenAI) are compared below. Here is how they stack up on benchmarks, price, and capabilities, and which one to pick in 2026.
Claude Sonnet 5 outperforms in 1 benchmark (Humanity's Last Exam), while GPT-5.6 Luna is better at 2 benchmarks (AutomationBench-AA, DeepSWE 1.1).
GPT-5.6 Luna is about 17.8× cheaper on a blended 3:1 input/output basis ($0.23 vs $4.00 per 1M tokens).
Choose Claude Sonnet 5 if…
- • your own prompt tests favor its output; shared comparable evidence does not identify a unique advantage
Choose GPT-5.6 Luna if…
- • you want the model leading more of the 4 shared benchmarks
- • lower blended API cost matters for your workload
The benchmark count includes only results measured with a matching benchmark version and protocol. Arena scores are shown separately. Missing, preliminary, and incompatible data is not treated as a controlled win. Published point-score comparisons are labeled separately when protocol details are incomplete. For text-output models, the verdict also compares token pricing and context windows.
Performance benchmarks
Every value links to its source. A dash means that no reviewed result is available for that exact model and protocol.
| Benchmark | Claude Sonnet 5 | GPT-5.6 Luna |
|---|---|---|
A 657-task benchmark of multi-step work across simulated SaaS applications in six business domains. The Artificial Analysis protocol reports a guardrail-aware score and is distinct from both the public Zapier split and the unrelated dynamic AutoBench framework. Guardrail-aware score | 39.2% Artificial Analysis | 42.2% Artificial Analysis |
A benchmark of difficult, verifiable information-seeking questions designed to measure an agent's ability to locate hard-to-find facts through web browsing. Accuracy | — | — |
A verified computer-use benchmark in which multimodal agents operate desktop applications and are graded from the resulting environment state. Mean task reward | — | — |
A long-horizon software-engineering benchmark with 113 original tasks graded by hand-written tests. Pass@1 | 54.0%±4.0 DataCurve | 67.0%±4.0 DataCurve |
A human-validated subset of real GitHub issues used to measure whether a coding agent can produce repository patches that resolve the associated tests. Resolved | — | — |
Version 2.1 of the benchmark for completing realistic tasks in terminal environments. Harness, resource limits, and attempt count are part of the protocol. Mean task success Protocols differ or are incompletely disclosed; not counted as a controlled win | 74.6%±1.6 Terminal-Bench | 75.7%±1.3 Terminal-Bench |
The highest-quality subset of Graduate-Level Google-Proof Q&A, designed to test expert-level scientific reasoning in biology, physics, and chemistry. Accuracy | 91.1% Artificial Analysis | 91.1% Artificial Analysis |
A 2,500-question expert-level benchmark spanning dozens of academic fields. Tool-assisted and no-tools results are separate protocols and must not be merged. Accuracy | 41.3% Artificial Analysis | 39.5% Artificial Analysis |
A contamination-resistant benchmark refreshed on a fixed release cadence. Scores from different LiveBench releases must never be compared as the same protocol. Mean of category averages Protocols differ or are incompletely disclosed; not counted as a controlled win | 76.0% LiveBench | 73.6% LiveBench |
Benchmark sources
- AutomationBench-AA: Agentic SaaS Workflow Benchmark
- DeepSWE 1.1 Leaderboard
- terminal-bench@2.1 Leaderboard
- GPQA Diamond Benchmark Leaderboard
- Humanity's Last Exam Benchmark Leaderboard
- LiveBench 2026-06-25 Leaderboard
Reviewed evidence last updated 2026-08-09.
Pricing, capabilities, and model facts
| Feature | Claude Sonnet 5 | GPT-5.6 Luna |
|---|---|---|
| Context & model facts | ||
| Developer | Anthropic | OpenAI |
| API provider | Anthropic | OpenAI |
| Input context | 1,000,000 tokens | 1,050,000 tokens |
| Maximum output | 128,000 tokens | 128,000 tokens |
| Released | — | — |
| Added to Writingmate | Jun 30, 2026 | Jul 9, 2026 |
| License | — | — |
| Knowledge cutoff | — | 2026-02-16 |
| Capabilities | ||
| Inputs | Text, Image, File | File, Image, Text |
| Outputs | Text | Text |
| Tool use | Yes | Yes |
| Reasoning | Yes | Yes |
| Vision | Yes | Yes |
| Image Generation | No | No |
| Video Generation | No | No |
| API pricing | ||
| Input (per 1M tokens) | $2.00 | $0.10 |
| Output (per 1M tokens) | $10.00 | $0.60 |
| Blended 3:1 input/output | $4.00 | $0.22 |
| API performance | ||
| p95 latency | Not measured | Not measured |
| Output throughput | Not measured | Not measured |
| Writingmate shows API performance only when both models have enough observations from the same measurement window, prompt profile, and provider. Third-party latency values are not copied into this table. | ||
Data sources
- Writingmate model catalog (pricing, limits, and availability)
Catalog data last updated Jul 9, 2026.
Why Pay for Multiple Subscriptions?
Comparing Claude Sonnet 5 from Anthropic with GPT-5.6 Luna from OpenAI? Instead of managing separate API keys and subscriptions, get both with Writingmate.
| Plan | Price | Claude Sonnet 5 | GPT-5.6 Luna | AI Images | AI Video |
|---|---|---|---|---|---|
Writingmate Pro Most popular | $20/mo | Included | Included | Nano Banana Pro, FLUX.2, DALL-E & more | Sora 2, VEO 3.1 |
Writingmate Ultimate Power users | $60/mo | Included | Included | Nano Banana Pro, FLUX.2, DALL-E & more | Sora 2, VEO 3.1 |
Claude Sonnet 5 vs GPT-5.6 Luna FAQ
Which is better, Claude Sonnet 5 or GPT-5.6 Luna?
Claude Sonnet 5 outperforms in 1 benchmark (Humanity's Last Exam), while GPT-5.6 Luna is better at 2 benchmarks (AutomationBench-AA, DeepSWE 1.1). GPT-5.6 Luna is about 17.8× cheaper on a blended 3:1 input/output basis ($0.23 vs $4.00 per 1M tokens).
Which model is cheaper to use through an API?
GPT-5.6 Luna is about 17.8× cheaper on a blended 3:1 input/output basis ($0.23 vs $4.00 per 1M tokens).
Which model supports more context?
The published context windows are close enough that this page does not treat the difference as a material advantage.
Can I switch between Claude Sonnet 5 and GPT-5.6 Luna?
Yes. Use the model selector on this page to open any current Writingmate model comparison. You can also run the same prompt with both models in Writingmate.