Claude Sonnet 5.5 vs GPT-6 Astra vs GPT-6.1 Sol
GPT-6.1 Sol comes out ahead, 69 to 65 and 64 on our weighted score.
AnthropicClaude Sonnet 5.5
65/100- ECI165.2
- Price$2.00 / $10.00
- Context1M
OpenAIGPT-6 Astra
64/100- ECI166.5
- Price$10.00 / $50.00
- Context1.05M
- Our pickOpenAI
GPT-6.1 Sol
69/100- ECI—
- Price$2.00 / $10.00
- Context1.05M
GPT-6.1 Sol is our pick
GPT-6.1 Sol is the better all-round choice, scoring 69/100 against Claude Sonnet 5.5 (65) and GPT-6 Astra (64). The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (GPQA Diamond, FrontierMath Tiers 1–3, OTIS Mock AIME 2024–2025 and SimpleQA Verified), because GPT-6.1 Sol has no Capabilities Index score yet.
- CapabilityGPT-6 AstraShared benchmarks: GPT-6 Astra 91.3% · GPT-6.1 Sol 90.7% · Claude Sonnet 5.5 82.7%
- Lowest priceClaude Sonnet 5.5 and GPT-6.1 SolClaude Sonnet 5.5 $4.00 · GPT-6.1 Sol $4.00 · GPT-6 Astra $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6 Astra and GPT-6.1 SolGPT-6 Astra 1,050,000 · GPT-6.1 Sol 1,050,000 · Claude Sonnet 5.5 1,000,000 tokens
- Widest inputsSame inputsClaude Sonnet 5.5: Text, Images, PDFs · GPT-6 Astra: Text, Images, PDFs · GPT-6.1 Sol: Text, Images, PDFs
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | Claude Sonnet 5.5 | GPT-6 Astra | GPT-6.1 Sol |
|---|---|---|---|---|
| CapabilityShared benchmarks | 50% | 83 | 91 | 91 |
| Price | 25% | 21 | 0 | 21 |
| Inputs & features | 15% | 80 | 80 | 80 |
| Context window | 10% | 60 | 61 | 61 |
| Overall | 100% | 65/100 | 64/100 | 69/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Sonnet 5.5Anthropic | GPT-6 AstraOpenAI | GPT-6.1 SolOpenAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 165.2 | 166.5 (best) | — |
| ECI rank | #3 of 148 | #2 of 148 (best) | — |
| GPQA DiamondGraduate-level science questions | 95.6% | 95.8% (best) | 95.4% |
| FrontierMath Tiers 1–3Research-level mathematics | 88.8% | 93.7% (best) | 93.7% (best) |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% | 100% | 100% |
| SimpleQA VerifiedShort factual questions | 46.5% | 75.6% (best) | 73.9% |
| Price per million tokens | |||
| Input | $2.00 (best) | $10.00 | $2.00 (best) |
| Output | $10.00 (best) | $50.00 | $10.00 (best) |
| Cached input | $0.20 | $1.00 | $0.10 (best) |
| Blended (3:1) | $4.00 (best) | $20.00 | $4.00 (best) |
| Long-context rate | Same rate | Over 272K: $20.00 / $75.00 | Over 272K: $4.00 / $15.00 |
| Price source | Official Anthropic API | Official OpenAI API | Official OpenAI API |
| Limits | |||
| Context window | 1,000,000 tokens | 1,050,000 tokens (best) | 1,050,000 tokens (best) |
| Max output | 128,000 tokens | 128,000 tokens | 128,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | Yes |
| Audio | No | No | No |
| Video | No | No | No |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | claude-sonnet-5-5 | gpt-6-astra | gpt-6.1-sol |
| API providers | 23 | 26 (best) | 21 |
| Released | Sep 28, 2026 | Sep 4, 2026 | Sep 29, 2026 |
| Knowledge cutoff | Jun 2026 | Apr 30, 2026 | Apr 30, 2026 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Claude Sonnet 5.5$40.00
- GPT-6 Astra$200.00
- GPT-6.1 Sol$40.00
Which should you choose?
Which is better: Claude Sonnet 5.5, GPT-6 Astra or GPT-6.1 Sol?
GPT-6.1 Sol is the better all-round choice, scoring 69/100 against Claude Sonnet 5.5 (65) and GPT-6 Astra (64). The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (GPQA Diamond, FrontierMath Tiers 1–3, OTIS Mock AIME 2024–2025 and SimpleQA Verified), because GPT-6.1 Sol has no Capabilities Index score yet.
Which is cheaper, Claude Sonnet 5.5, GPT-6 Astra or GPT-6.1 Sol?
Claude Sonnet 5.5 is cheaper at $2.00 input / $10.00 output per million tokens (official Anthropic API price). GPT-6.1 Sol costs $2.00 input / $10.00 output per million tokens (official OpenAI API price); GPT-6 Astra costs $10.00 input / $50.00 output per million tokens (official OpenAI API price). At a typical mix of three input tokens to one output token, that is $4.00 per million tokens for Claude Sonnet 5.5 versus $4.00 for GPT-6.1 Sol (1× as much) and $20.00 for GPT-6 Astra (5× as much).
Which scores higher on benchmarks?
Not every model here has a Capabilities Index score, so we compare the average of shared benchmarks (GPQA Diamond, FrontierMath Tiers 1–3, OTIS Mock AIME 2024–2025 and SimpleQA Verified): GPT-6 Astra 91.3%, GPT-6.1 Sol 90.7% and Claude Sonnet 5.5 82.7%. On individual benchmarks: GPQA Diamond — GPT-6 Astra 95.8%, Claude Sonnet 5.5 95.6%, GPT-6.1 Sol 95.4%; FrontierMath Tiers 1–3 — GPT-6 Astra 93.7%, GPT-6.1 Sol 93.7%, Claude Sonnet 5.5 88.8%; OTIS Mock AIME 2024–2025 — Claude Sonnet 5.5 100%, GPT-6 Astra 100%, GPT-6.1 Sol 100%; SimpleQA Verified — GPT-6 Astra 75.6%, GPT-6.1 Sol 73.9%, Claude Sonnet 5.5 46.5%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Sonnet 5.5, GPT-6 Astra and GPT-6.1 Sol yet, so there is no like-for-like coding score. On overall capability, GPT-6 Astra leads, which tends to carry over to coding, but test on your own codebase. All three support tool calling for agent workflows.
Which has the bigger context window?
GPT-6 Astra and GPT-6.1 Sol have the largest context windows (1,050,000 and 1,050,000 tokens), against 1,000,000 for Claude Sonnet 5.5. Maximum output per response: Claude Sonnet 5.5 up to 128,000, GPT-6 Astra up to 128,000, GPT-6.1 Sol up to 128,000 tokens.
Which can read images, PDFs, audio or video?
Claude Sonnet 5.5 accepts text, images and PDFs; GPT-6 Astra accepts text, images and PDFs; GPT-6.1 Sol accepts text, images and PDFs. They handle the same number of input types.
Are any of these open source?
No. Claude Sonnet 5.5, GPT-6 Astra and GPT-6.1 Sol are proprietary and only available through APIs and apps.
Which is newer?
GPT-6.1 Sol is the newest, released Sep 29, 2026. Claude Sonnet 5.5 came out Sep 28, 2026; GPT-6 Astra came out Sep 4, 2026. Knowledge cutoff: Claude Sonnet 5.5 Jun 2026, GPT-6 Astra Apr 30, 2026, GPT-6.1 Sol Apr 30, 2026.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
