Claude Opus 5.5 vs Kimi K3 vs GPT-6 Astra
Too close to call on our weighted score (Claude Opus 5.5 70, GPT-6 Astra 68, Kimi K3 65). The right pick depends on what you value most.
AnthropicClaude Opus 5.5
70/100- ECI167.4
- Price$4.00 / $20.00
- Context1M
Moonshot AIKimi K3
65/100- ECI157.6
- Price$3.00 / $15.00
- Context1.05M
OpenAIGPT-6 Astra
68/100- ECI166.5
- Price$10.00 / $50.00
- Context1.05M
Too close to call
It is close. Our weighted score puts them within 2 points (Claude Opus 5.5 70/100, GPT-6 Astra 68/100, Kimi K3 65/100), so choose by what matters most for your work: Claude Opus 5.5 for raw capability and Kimi K3 on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityClaude Opus 5.5Capabilities Index (ECI): Claude Opus 5.5 167.4 · GPT-6 Astra 166.5 · Kimi K3 157.6
- Lowest priceKimi K3Kimi K3 $6.00 · Claude Opus 5.5 $8.00 · GPT-6 Astra $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6 Astra and Kimi K3GPT-6 Astra 1,050,000 · Kimi K3 1,048,576 · Claude Opus 5.5 1,000,000 tokens
- Widest inputsSame inputsClaude Opus 5.5: Text, Images, PDFs · Kimi K3: Text, Images, Video · GPT-6 Astra: Text, Images, PDFs
- Self-hostingKimi K3Publishes downloadable weights
| Measure | Weight | Claude Opus 5.5 | Kimi K3 | GPT-6 Astra |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 100 | 88 | 99 |
| Price | 25% | 7 | 13 | 0 |
| Inputs & features | 15% | 80 | 80 | 80 |
| Context window | 10% | 60 | 61 | 61 |
| Overall | 100% | 70/100 | 65/100 | 68/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Opus 5.5Anthropic | Kimi K3Moonshot AI | GPT-6 AstraOpenAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 167.4 (best) | 157.6 | 166.5 |
| ECI rank | #1 of 148 (best) | #13 of 148 | #2 of 148 |
| GPQA DiamondGraduate-level science questions | 90.6% | 93.1% | 95.8% (best) |
| FrontierMath Tiers 1–3Research-level mathematics | 91.2% | 72.2% | 93.7% (best) |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% (best) | 97.2% | 100% (best) |
| SimpleQA VerifiedShort factual questions | 72.2% | 50.6% | 75.6% (best) |
| Price per million tokens | |||
| Input | $4.00 | $3.00 (best) | $10.00 |
| Output | $20.00 | $15.00 (best) | $50.00 |
| Cached input | $0.20 (best) | $0.30 | $1.00 |
| Blended (3:1) | $8.00 | $6.00 (best) | $20.00 |
| Long-context rate | Same rate | Same rate | Over 272K: $20.00 / $75.00 |
| Price source | Official Anthropic API | Official Moonshot AI API | Official OpenAI API |
| Limits | |||
| Context window | 1,000,000 tokens | 1,048,576 tokens | 1,050,000 tokens (best) |
| Max output | 128,000 tokens | 131,072 tokens (best) | 128,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | No | Yes |
| Audio | No | No | No |
| Video | No | Yes | No |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · high · max | Yeslow · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Open | Proprietary |
| API model ID | claude-opus-5-5 | kimi-k3 | gpt-6-astra |
| API providers | 28 | 68 (best) | 26 |
| Released | Sep 22, 2026 | Jul 16, 2026 | Sep 4, 2026 |
| Knowledge cutoff | Jun 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 Opus 5.5$80.00
- Kimi K3$60.00
- GPT-6 Astra$200.00
Which should you choose?
Which is better: Claude Opus 5.5, Kimi K3 or GPT-6 Astra?
It is close. Our weighted score puts them within 2 points (Claude Opus 5.5 70/100, GPT-6 Astra 68/100, Kimi K3 65/100), so choose by what matters most for your work: Claude Opus 5.5 for raw capability and Kimi K3 on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Claude Opus 5.5, Kimi K3 or GPT-6 Astra?
Kimi K3 is cheaper at $3.00 input / $15.00 output per million tokens (official Moonshot AI API price). Claude Opus 5.5 costs $4.00 input / $20.00 output per million tokens (official Anthropic 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 $6.00 per million tokens for Kimi K3 versus $8.00 for Claude Opus 5.5 (1.3× as much) and $20.00 for GPT-6 Astra (3.3× as much).
Which scores higher on benchmarks?
Claude Opus 5.5 scores higher on the Capabilities Index (ECI): Claude Opus 5.5 167.4 (#1 of 148), GPT-6 Astra 166.5 (#2 of 148) and Kimi K3 157.6 (#13 of 148). The confidence ranges of the top two overlap (164.0–172.0 vs 163.1–171.1), so treat the gap as small. On individual benchmarks: GPQA Diamond — GPT-6 Astra 95.8%, Kimi K3 93.1%, Claude Opus 5.5 90.6%; FrontierMath Tiers 1–3 — GPT-6 Astra 93.7%, Claude Opus 5.5 91.2%, Kimi K3 72.2%; OTIS Mock AIME 2024–2025 — Claude Opus 5.5 100%, GPT-6 Astra 100%, Kimi K3 97.2%; SimpleQA Verified — GPT-6 Astra 75.6%, Claude Opus 5.5 72.2%, Kimi K3 50.6%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Opus 5.5, Kimi K3 and GPT-6 Astra yet, so there is no like-for-like coding score. On overall capability, Claude Opus 5.5 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 Kimi K3 have the largest context windows (1,050,000 and 1,048,576 tokens), against 1,000,000 for Claude Opus 5.5. Maximum output per response: Claude Opus 5.5 up to 128,000, Kimi K3 up to 131,072, GPT-6 Astra up to 128,000 tokens.
Which can read images, PDFs, audio or video?
Claude Opus 5.5 accepts text, images and PDFs; Kimi K3 accepts text, images and video; GPT-6 Astra accepts text, images and PDFs. They handle the same number of input types.
Are any of these open source?
Kimi K3 publishes its weights and can be self-hosted; Claude Opus 5.5 and GPT-6 Astra is proprietary.
Which is newer?
Claude Opus 5.5 is the newest, released Sep 22, 2026. GPT-6 Astra came out Sep 4, 2026; Kimi K3 came out Jul 16, 2026. Knowledge cutoff: Claude Opus 5.5 Jun 2026, GPT-6 Astra 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.
