GPT-6 Astra (Fast) vs Claude Mythos 5 vs Kimi K2.8 Preview
Too close to call on our weighted score (GPT-6 Astra (Fast) 72, Claude Mythos 5 72, Kimi K2.8 Preview 66). The right pick depends on what you value most.
OpenAIGPT-6 Astra (Fast)
72/100- ECI—
- Price$20.00 / $100.00
- Context1.05M
AnthropicClaude Mythos 5
72/100- ECI—
- Price$10.00 / $50.00
- Context1M
Moonshot AIKimi K2.8 Preview
66/100- ECI—
- Price—
- Context1.05M
Too close to call
It is close. Our weighted score puts them within a point (GPT-6 Astra (Fast) 72/100, Claude Mythos 5 72/100, Kimi K2.8 Preview 66/100), so choose by what matters most for your work: Claude Mythos 5 on price. The score weighs inputs & features 60%, context window 40%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
- CapabilityNot enough dataNo independent benchmark covers every model here yet
- Lowest priceClaude Mythos 5Claude Mythos 5 $20.00 · GPT-6 Astra (Fast) $40.00 per 1M tokens (3:1 blend) · Kimi K2.8 Preview unpriced
- Longest contextGPT-6 Astra (Fast) and Kimi K2.8 PreviewGPT-6 Astra (Fast) 1,050,000 · Kimi K2.8 Preview 1,048,576 · Claude Mythos 5 1,000,000 tokens
- Widest inputsSame inputsGPT-6 Astra (Fast): Text, Images, PDFs · Claude Mythos 5: Text, Images, PDFs · Kimi K2.8 Preview: Text, Images, Video
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | GPT-6 Astra (Fast) | Claude Mythos 5 | Kimi K2.8 Preview |
|---|---|---|---|---|
| Inputs & features | 60% | 80 | 80 | 70 |
| Context window | 40% | 61 | 60 | 61 |
| Overall | 100% | 72/100 | 72/100 | 66/100 |
Left out because at least one model lacks the data: capability and price. The remaining weights were rescaled.
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | GPT-6 Astra (Fast)OpenAI | Claude Mythos 5Anthropic | Kimi K2.8 PreviewMoonshot AI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | — | — | — |
| ECI rank | — | — | — |
| Price per million tokens | |||
| Input | $20.00 | $10.00 (best) | — |
| Output | $100.00 | $50.00 (best) | — |
| Cached input | — | — | — |
| Blended (3:1) | $40.00 | $20.00 (best) | — |
| Long-context rate | Same rate | Same rate | — |
| Price source | Median of 1 providers | Median of 2 providers | — |
| Limits | |||
| Context window | 1,050,000 tokens (best) | 1,000,000 tokens | 1,048,576 tokens |
| Max output | 128,000 tokens | 128,000 tokens | — |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | No |
| Audio | No | No | No |
| Video | No | No | Yes |
| Reasoning | Yes | Yes | Yes |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | No |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | — | — | — |
| API providers | 1 | 2 (best) | — |
| Released | Sep 4, 2026 | Jun 9, 2026 | Sep 11, 2026 |
| Knowledge cutoff | — | Jan 31, 2026 | — |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- GPT-6 Astra (Fast)$400.00
- Claude Mythos 5$200.00
- Kimi K2.8 Preview—
Which should you choose?
Which is better: GPT-6 Astra (Fast), Claude Mythos 5 or Kimi K2.8 Preview?
It is close. Our weighted score puts them within a point (GPT-6 Astra (Fast) 72/100, Claude Mythos 5 72/100, Kimi K2.8 Preview 66/100), so choose by what matters most for your work: Claude Mythos 5 on price. The score weighs inputs & features 60%, context window 40%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
Which is cheaper, GPT-6 Astra (Fast), Claude Mythos 5 or Kimi K2.8 Preview?
Claude Mythos 5 is cheaper at $10.00 input / $50.00 output per million tokens (median across 2 API providers). GPT-6 Astra (Fast) costs $20.00 input / $100.00 output per million tokens (median across 1 API provider). At a typical mix of three input tokens to one output token, that is $20.00 per million tokens for Claude Mythos 5 versus $40.00 for GPT-6 Astra (Fast) (2× as much). Kimi K2.8 Preview has no published per-token price.
Which scores higher on benchmarks?
There is no independent benchmark that covers all three models yet. GPT-6 Astra (Fast) has not been scored yet, Claude Mythos 5 has not been scored yet and Kimi K2.8 Preview has not been scored yet.
Which is better for coding?
There are no published SWE-bench Verified results for GPT-6 Astra (Fast), Claude Mythos 5 and Kimi K2.8 Preview yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. All three support tool calling for agent workflows.
Which has the bigger context window?
GPT-6 Astra (Fast) and Kimi K2.8 Preview have the largest context windows (1,050,000 and 1,048,576 tokens), against 1,000,000 for Claude Mythos 5. Maximum output per response: GPT-6 Astra (Fast) up to 128,000, Claude Mythos 5 up to 128,000 tokens.
Which can read images, PDFs, audio or video?
GPT-6 Astra (Fast) accepts text, images and PDFs; Claude Mythos 5 accepts text, images and PDFs; Kimi K2.8 Preview accepts text, images and video. They handle the same number of input types.
Are any of these open source?
No. GPT-6 Astra (Fast), Claude Mythos 5 and Kimi K2.8 Preview are proprietary and only available through APIs and apps.
Which is newer?
Kimi K2.8 Preview is the newest, released Sep 11, 2026. GPT-6 Astra (Fast) came out Sep 4, 2026; Claude Mythos 5 came out Jun 9, 2026. Knowledge cutoff: Claude Mythos 5 Jan 31, 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.
