Which is cheaper, Claude Fable 5.1 and GPT-6 Luna?

GPT-6 Luna has the lowest input price. Per 1M input tokens: Claude Fable 5.1 from $10.00 and GPT-6 Luna from $0.10.

Which has the larger context window, Claude Fable 5.1 and GPT-6 Luna?

Claude Fable 5.1 has the largest context window: Claude Fable 5.1 1,000,000 tokens and GPT-6 Luna 400,000 tokens.

Which is smarter, Claude Fable 5.1 and GPT-6 Luna?

Claude Fable 5.1 scores highest on the Artificial Analysis Intelligence Index: Claude Fable 5.1 51.2 and GPT-6 Luna 38.1.

Can I switch between Claude Fable 5.1 and GPT-6 Luna without changing my code?

Yes. All of them are served through FastRouter's OpenAI-compatible API, so switching is a change of the model parameter (anthropic/claude-fable-5.1, openai/gpt-6-luna).

Claude Fable 5.1 vs GPT-6 Luna

Side-by-side pricing per provider, context window, benchmark scores and speed, all on one OpenAI-compatible API.

Claude Fable 5.1 Anthropicanthropic/claude-fable-5.1

GPT-6 Luna OpenAIopenai/gpt-6-luna

Creator

Anthropic

OpenAI

Released

Sep 1, 2026

Sep 22, 2026

Context window

400K

Max output

128K

Input / 1MLowest provider price

$10.00

$0.10

Output / 1MLowest provider price

$50.00

$0.50

Providers

IntelligenceArtificial Analysis index

51.2

38.1

CodingArtificial Analysis index

79.1

—

Accepts

Text, Image, Files

Files, Image, Text

Produces

Text

Tool calling

Yes

Structured output

Yes

Reasoning

Yes

Claude Fable 5.1 vs GPT-6 Luna: summary

Claude Fable 5.1 and GPT-6 Luna are both available through FastRouter's OpenAI-compatible API, so switching between them is a change of model id, not a new integration.

Claude Fable 5.1, from Anthropic, has a 1,000,000-token context window, costs $10.00/1M input and $50.00/1M output tokens and scores 51.2 on the Artificial Analysis Intelligence Index.

GPT-6 Luna, from OpenAI, has a 400,000-token context window, costs $0.10/1M input and $0.50/1M output tokens and scores 38.1 on the Artificial Analysis Intelligence Index.

GPT-6 Luna is the cheapest on input, 100× cheaper than the next model, Claude Fable 5.1 has the largest context window and Claude Fable 5.1 scores highest for intelligence.

Switch with one line

client = OpenAI(base_url="https://api.fastrouter.ai/api/v1", api_key="<FASTROUTER_API_KEY>") client.chat.completions.create(model="anthropic/claude-fable-5.1", messages=[...]) # or client.chat.completions.create(model="openai/gpt-6-luna", messages=[...])

Full API docs

Frequently asked questions

More comparisons

Benchmark scores sourced from ArtificialAnalysis