# Claude Fable 5

Claude Fable 5 is a text generation model from Anthropic, available through the Impossibl API. Its published context window is 1,000,000 tokens. The advertised input rate is $10.00 per million input tokens. The advertised output rate is $50.00 per million output tokens.

- Model identifier: ` anthropic/claude-fable-5 `
- Creator: Anthropic
- Model type: Text generation
- Canonical model page: [Claude Fable 5](<https://impossibl.com/anthropic/claude-fable-5>)
- API availability: Listed as serving through Impossibl.
- Creator release date: 2026-06-09

## Capabilities and limits

- Context window: 1,000,000 tokens
- Maximum output tokens: Not published in the public catalog; this is separate from the context window.
- Inputs: text, image
- Outputs: text
- Tool calling: Not published

## API access

Use ` anthropic/claude-fable-5 ` as the model identifier through the Impossibl API.

Published API endpoints:

- ` /v1/chat/completions `

[API quickstart](<https://impossibl.com/docs/agent-quickstart>) · [Models and billing documentation](<https://impossibl.com/docs/models>)

## Published API prices

All rates are in USD. An unpublished rate is unknown, not zero. Workspace-specific pricing, taxes, balance-purchase fees, billing adjustments, and tool charges can affect the amount paid.

| Usage | Published base rate | Billing unit |
| --- | --- | --- |
| Input | $10.00 | per million input tokens |
| Output | $50.00 | per million output tokens |
| Cache read | $1.00 | per million cached input tokens |
| Cache write (default retention) | $12.50 | per million tokens |
| Cache write (one-hour retention) | $20.00 | per million tokens |
| Audio input | Not published | per million audio input tokens |

## Independent benchmarks

Source: [Artificial Analysis](<https://artificialanalysis.ai/>). Last checked: 2026-09-11T10:50:14.034Z.
Configurations are evaluated separately. API scores retain their original units. Unmeasured scores are omitted.

### Claude Fable 5 (Adaptive Reasoning, Max Effort, Opus 4.8 Fallback)

Source: [Evaluation source](<https://artificialanalysis.ai/models/claude-fable-5>)

| Benchmark | Score |
| --- | --- |
| Intelligence Index | 49.70 |
| Omniscience Index | 43.30 |
| GPQA | 92.63% |
| Humanity’s Last Exam | 55.47% |
| SciCode | 61.00% |
| CritPt | 28.57% |
| Terminal-Bench v2.1 | 84.64% |
| Terminal-Bench v4.0 | 42.42% |
| Terminal-Bench Hard | 62.88% |
| AA-LCR | 82.33% |
| Multilingual LCR | 64.44% |
| Harvey LAB | 93.56% |
| GDPval Elo | 1631.46 |
| GDP.pdf All-pass | 24.00% |
| AutomationBench Partial | 54.07% |
| AnalystAgent | 48.75% |
| IFBench | 63.47% |
| Tau2 | 98.54% |
| Tau Banking | 38.14% |
| coding index (API) | 76.5 |
| agentic index (API) | 51 |
| intelligence index (API) | 49.7 |

Full benchmark data and breakdowns: [Complete benchmark snapshot](<https://api.impossibl.com/v1/models/anthropic/claude-fable-5/benchmarks>).


## Availability and retirement

The model is listed as serving. No retirement is announced in the current public catalog.

## Frequently asked questions

### What is Claude Fable 5?

Claude Fable 5 is a text-generation model from Anthropic, available through the Impossibl API.

### How much does Claude Fable 5 cost?

Claude Fable 5 costs $10.00 per million input tokens and $50.00 per million output tokens through the Impossibl API. Cache reads cost $1.00 per million tokens; cache writes cost $12.50 per million tokens; cache writes with one-hour retention cost $20.00 per million tokens. All rates are in USD.

### What is the context length of Claude Fable 5?

Claude Fable 5 has a 1,000,000-token context window through the Impossibl API.

### What inputs and outputs does Claude Fable 5 support?

Claude Fable 5 accepts text and image as input. Claude Fable 5 returns text.

### How do I use Claude Fable 5 through an API?

Claude Fable 5 is available through the Impossibl API. Use anthropic/claude-fable-5 as the model identifier with /v1/chat/completions. The quickstart explains how to create an API key and send your first request.

### When was Claude Fable 5 released?

Anthropic released Claude Fable 5 on June 9, 2026.

Sources: [Creator release announcement](<https://www.anthropic.com/news/claude-fable-5-mythos-5>)

## Sources and related links

Prices, limits, capabilities, endpoints, and availability come from the public Impossibl catalog. Creator documentation supplies descriptions and release dates where available; it does not override the published API offering.

- [Public Impossibl model catalog](<https://api.impossibl.com/v1/models>)
- [Full model directory as JSON](<https://impossibl.com/models.json>)
- [Claude Fable 5: model details and pricing](<https://impossibl.com/anthropic/claude-fable-5>)
- [Model directory](<https://impossibl.com/models>)