Claude Opus 4.8 vs GPT-6 Astra vs GPT-5.5
GPT-6 Astra comes out ahead, 68 to 63 and 63 on our weighted score, though Claude Opus 4.8 is 2× cheaper per token.
AnthropicClaude Opus 4.8
63/100- ECI158.3
- Price$5.00 / $25.00
- Context1M
- Our pick
OpenAIGPT-6 Astra
68/100- ECI166.5
- Price$10.00 / $50.00
- Context1.05M
- OpenAI
GPT-5.5
63/100- ECI159.2
- Price$5.00 / $30.00
- Context1.05M
GPT-6 Astra is our pick
GPT-6 Astra is the better all-round choice, scoring 68/100 against GPT-5.5 (63) and Claude Opus 4.8 (63). It leads on capability. Claude Opus 4.8 wins on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGPT-6 AstraCapabilities Index (ECI): GPT-6 Astra 166.5 · GPT-5.5 159.2 · Claude Opus 4.8 158.3
- Lowest priceClaude Opus 4.8Claude Opus 4.8 $10.00 · GPT-5.5 $11.25 · GPT-6 Astra $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6 Astra and GPT-5.5GPT-6 Astra 1,050,000 · GPT-5.5 1,050,000 · Claude Opus 4.8 1,000,000 tokens
- Widest inputsSame inputsClaude Opus 4.8: Text, Images, PDFs · GPT-6 Astra: Text, Images, PDFs · GPT-5.5: Text, Images, PDFs
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | Claude Opus 4.8 | GPT-6 Astra | GPT-5.5 |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 89 | 99 | 90 |
| Price | 25% | 2 | 0 | 0 |
| Inputs & features | 15% | 80 | 80 | 80 |
| Context window | 10% | 60 | 61 | 61 |
| Overall | 100% | 63/100 | 68/100 | 63/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Opus 4.8Anthropic | GPT-6 AstraOpenAI | GPT-5.5OpenAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 158.3 | 166.5 (best) | 159.2 |
| ECI rank | #12 of 148 | #2 of 148 (best) | #10 of 148 |
| GPQA DiamondGraduate-level science questions | 91.0% | 95.8% (best) | 94.0% |
| FrontierMath Tiers 1–3Research-level mathematics | 80.0% | 93.7% (best) | 85.3% |
| OTIS Mock AIME 2024–2025Competition mathematics | 98.3% | 100% (best) | 100% (best) |
| SWE-bench VerifiedFixing real GitHub issues | — | — | 80.6% |
| SimpleQA VerifiedShort factual questions | 53.0% | 75.6% (best) | 63.0% |
| Price per million tokens | |||
| Input | $5.00 (best) | $10.00 | $5.00 (best) |
| Output | $25.00 (best) | $50.00 | $30.00 |
| Cached input | $0.50 (best) | $1.00 | $0.50 (best) |
| Blended (3:1) | $10.00 (best) | $20.00 | $11.25 |
| Long-context rate | Same rate | Over 272K: $20.00 / $75.00 | Over 272K: $10.00 / $45.00 |
| 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 |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | claude-opus-4-8 | gpt-6-astra | gpt-5.5 |
| API providers | 45 (best) | 26 | 42 |
| Released | May 28, 2026 | Sep 4, 2026 | Apr 23, 2026 |
| Knowledge cutoff | Jan 2026 | Apr 30, 2026 | Dec 1, 2025 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Claude Opus 4.8$100.00
- GPT-6 Astra$200.00
- GPT-5.5$110.00
Which should you choose?
Which is better: Claude Opus 4.8, GPT-6 Astra or GPT-5.5?
GPT-6 Astra is the better all-round choice, scoring 68/100 against GPT-5.5 (63) and Claude Opus 4.8 (63). It leads on capability. Claude Opus 4.8 wins on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Claude Opus 4.8, GPT-6 Astra or GPT-5.5?
Claude Opus 4.8 is cheaper at $5.00 input / $25.00 output per million tokens (official Anthropic API price). GPT-5.5 costs $5.00 input / $30.00 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 $10.00 per million tokens for Claude Opus 4.8 versus $11.25 for GPT-5.5 (1.1× as much) and $20.00 for GPT-6 Astra (2× as much).
Which scores higher on benchmarks?
GPT-6 Astra scores higher on the Capabilities Index (ECI): GPT-6 Astra 166.5 (#2 of 148), GPT-5.5 159.2 (#10 of 148) and Claude Opus 4.8 158.3 (#12 of 148). Their confidence ranges do not overlap (163.1–171.1 vs 156.9–162.4), so the gap is a real one. On individual benchmarks: GPQA Diamond — GPT-6 Astra 95.8%, GPT-5.5 94.0%, Claude Opus 4.8 91.0%; FrontierMath Tiers 1–3 — GPT-6 Astra 93.7%, GPT-5.5 85.3%, Claude Opus 4.8 80.0%; OTIS Mock AIME 2024–2025 — GPT-6 Astra 100%, GPT-5.5 100%, Claude Opus 4.8 98.3%; SimpleQA Verified — GPT-6 Astra 75.6%, GPT-5.5 63.0%, Claude Opus 4.8 53.0%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Opus 4.8 and GPT-6 Astra 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-5.5 have the largest context windows (1,050,000 and 1,050,000 tokens), against 1,000,000 for Claude Opus 4.8. Maximum output per response: Claude Opus 4.8 up to 128,000, GPT-6 Astra up to 128,000, GPT-5.5 up to 128,000 tokens.
Which can read images, PDFs, audio or video?
Claude Opus 4.8 accepts text, images and PDFs; GPT-6 Astra accepts text, images and PDFs; GPT-5.5 accepts text, images and PDFs. They handle the same number of input types.
Are any of these open source?
No. Claude Opus 4.8, GPT-6 Astra and GPT-5.5 are proprietary and only available through APIs and apps.
Which is newer?
GPT-6 Astra is the newest, released Sep 4, 2026. Claude Opus 4.8 came out May 28, 2026; GPT-5.5 came out Apr 23, 2026. Knowledge cutoff: Claude Opus 4.8 Jan 2026, GPT-6 Astra Apr 30, 2026, GPT-5.5 Dec 1, 2025.
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.
