# Claude Fable 5.1 vs Inkling 256K

Canonical HTML page: [Claude Fable 5.1 vs Inkling 256K](<https://impossibl.com/compare/anthropic/claude-fable-5-1/thinkingmachines/inkling-256k>)
Markdown alternative: [Claude Fable 5.1 vs Inkling 256K as Markdown](<https://impossibl.com/compare/anthropic/claude-fable-5-1/thinkingmachines/inkling-256k.md>)

Compare API pricing, context windows, and capabilities side by side. Prices are published API usage rates in USD; check billing units and context tiers alongside each price.

## Specifications and pricing

| Specification | Claude Fable 5.1 | Inkling 256K |
| --- | --- | --- |
| API identifier | anthropic/claude-fable-5-1 | thinkingmachines/inkling-256k |
| Creator | Anthropic | Thinking Machines |
| Model type | Text generation | Text generation |
| Inputs | text, image | text, image |
| Outputs | text | text |
| Base input price (USD) | $10.00 per million input tokens | $3.74 per million input tokens |
| Base output price (USD) | $50.00 per million output tokens | $9.36 per million output tokens |
| Cache read price (USD) | $0.25 per million cached input tokens | $0.748 per million cached input tokens |
| Cache write price (USD) | $12.50 per million tokens | Not published |
| One-hour cache write price (USD) | $20.00 per million tokens | Not published |
| Audio input token price (USD) | Not published | Not published |
| Context window | 1,000,000 tokens | 262,144 tokens |
| Tool calling | Not published | Not published |
| Endpoints | /v1/chat/completions | /v1/chat/completions |
| Context pricing tiers (USD per million tokens) | None published | None published |
| Retirement | Not announced in the public catalog | Not announced in the public catalog |

When total input, including cached input, strictly exceeds a context threshold, the highest qualifying tier applies to the whole request. Consult each model's complete Markdown for tier-specific cache rates; an unpublished tier cache price does not establish the base cache rate.

## Claude Fable 5.1 vs Inkling 256K: side-by-side summary

Claude Fable 5.1 and Inkling 256K are available through the Impossibl API.

They share the `/v1/chat/completions` endpoint. Set the model identifier to select the model for a supported request.

Claude Fable 5.1 is created by Anthropic. It has a 1,000,000-token context window. Base API pricing (USD): $10.00 per million input tokens; $50.00 per million output tokens.

Inkling 256K is created by Thinking Machines. It has a 262,144-token context window. Base API pricing (USD): $3.74 per million input tokens; $9.36 per million output tokens.

## Model details

- [Claude Fable 5.1: full model facts as Markdown](<https://impossibl.com/anthropic/claude-fable-5-1.md>); [HTML model page](<https://impossibl.com/anthropic/claude-fable-5-1>)
- [Inkling 256K: full model facts as Markdown](<https://impossibl.com/thinkingmachines/inkling-256k.md>); [HTML model page](<https://impossibl.com/thinkingmachines/inkling-256k>)

For compatible text or embedding models with token pricing, the HTML comparison page provides a shared workload calculator. It excludes cache creation, tool calls, taxes, balance-purchase fees, and workspace-specific adjustments.

## Sources and related links

Prices, capabilities, limits, and availability describe the public Impossibl API offering. An unpublished fact is unknown; a published zero price is zero. Compare matching billing units and check context tiers before estimating costs.

- [Public Impossibl model catalog](<https://api.impossibl.com/v1/models>)
- [Full model directory as JSON](<https://impossibl.com/models.json>)
- [Model directory as Markdown](<https://impossibl.com/models.md>)
- [API quickstart](<https://impossibl.com/docs/agent-quickstart>)
- [Model documentation](<https://impossibl.com/docs/models>)