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Comparison · 2 models · Updated Nov 2, 2026

Claude Mythos 5.1 vs GPT-6 Astra (Fast)

Too close to call on our weighted score (GPT-6 Astra (Fast) 66, Claude Mythos 5.1 66). The right pick depends on what you value most.

  1. Anthropic

    Claude Mythos 5.1

    Released Sep 1, 2026

    66/100
    • ECI—
    • Price—
    • Context1M
    Full specs Remove Claude Mythos 5.1

  2. OpenAI

    GPT-6 Astra (Fast)

    Released Sep 4, 2026New

    66/100
    • ECI—
    • Price$20.00 / $100.00
    • Context1.05M
    Full specs Remove GPT-6 Astra (Fast)

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01 — Verdict

Too close to call

It is close. Our weighted score puts them within a point (GPT-6 Astra (Fast) 66/100, Claude Mythos 5.1 66/100), so choose by what matters most for your work: GPT-6 Astra (Fast) on price and GPT-6 Astra (Fast) for long inputs. 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 priceGPT-6 Astra (Fast)GPT-6 Astra (Fast) $40.00 per 1M tokens (3:1 blend) · Claude Mythos 5.1 unpriced
  • Longest contextGPT-6 Astra (Fast)GPT-6 Astra (Fast) 1,050,000 · Claude Mythos 5.1 1,000,000 tokens
  • Widest inputsSame inputsClaude Mythos 5.1: Text, Images, PDFs · GPT-6 Astra (Fast): Text, Images, PDFs
  • Self-hostingNo open weightsBoth are available only through APIs
How the score is built
MeasureWeightClaude Mythos 5.1GPT-6 Astra (Fast)
Inputs & features60%7070
Context window40%6061
Overall100%66/10066/100

Left out because at least one model lacks the data: capability and price. The remaining weights were rescaled.

02 — Side by side

Every spec in one table

Highlighted cells lead their row. Dashes mean the data is not published.

Claude Mythos 5.1 vs GPT-6 Astra (Fast) specifications side by side
SpecificationClaude Mythos 5.1AnthropicGPT-6 Astra (Fast)OpenAI
Capability
Capabilities Index (ECI)——
ECI rank——
Price per million tokens
Input—$20.00
Output—$100.00
Cached input——
Blended (3:1)—$40.00
Long-context rate—Same rate
Price source—Median of 1 providers
Limits
Context window1,000,000 tokens1,050,000 tokens (best)
Max output128,000 tokens128,000 tokens
Inputs and features
TextYesYes
ImagesYesYes
PDFsYesYes
AudioNoNo
VideoNoNo
ReasoningYesYes
Tool callingYesYes
Structured outputNoNo
Availability
WeightsProprietaryProprietary
API model ID——
API providers—1
ReleasedSep 1, 2026Sep 4, 2026
Knowledge cutoffJun 2026—
03 — Cost

What would a month cost?

Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.

  • Claude Mythos 5.1—
  • GPT-6 Astra (Fast)$400.00
04 — Questions

Which should you choose?

Which is better: Claude Mythos 5.1 or GPT-6 Astra (Fast)?

It is close. Our weighted score puts them within a point (GPT-6 Astra (Fast) 66/100, Claude Mythos 5.1 66/100), so choose by what matters most for your work: GPT-6 Astra (Fast) on price and GPT-6 Astra (Fast) for long inputs. 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, Claude Mythos 5.1 or GPT-6 Astra (Fast)?

GPT-6 Astra (Fast) is cheaper at $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 $40.00 per million tokens for GPT-6 Astra (Fast) versus . Claude Mythos 5.1 has no published per-token price.

Which scores higher on benchmarks?

There is no independent benchmark that covers both models yet. Claude Mythos 5.1 has not been scored yet and GPT-6 Astra (Fast) has not been scored yet.

Which is better for coding?

There are no published SWE-bench Verified results for Claude Mythos 5.1 and GPT-6 Astra (Fast) yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. Both support tool calling for agent workflows.

Which has the bigger context window?

GPT-6 Astra (Fast) has the largest context window at 1,050,000 tokens, against 1,000,000 for Claude Mythos 5.1. Maximum output per response: Claude Mythos 5.1 up to 128,000, GPT-6 Astra (Fast) up to 128,000 tokens.

Which can read images, PDFs, audio or video?

Claude Mythos 5.1 accepts text, images and PDFs; GPT-6 Astra (Fast) accepts text, images and PDFs. They handle the same number of input types.

Are any of these open source?

No. Claude Mythos 5.1 and GPT-6 Astra (Fast) are proprietary and only available through APIs and apps.

Which is newer?

GPT-6 Astra (Fast) is the newest, released Sep 4, 2026. Claude Mythos 5.1 came out Sep 1, 2026. Knowledge cutoff: Claude Mythos 5.1 Jun 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 Nov 2, 2026.

05 — Keep comparing

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