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Claude Fable 5.1
Claude Fable 5.1 is Anthropic's flagship large language model released on September 1, 2026, positioned as the top choice for long-horizon agentic workflows, complex coding, and knowledge work. The model supports a 1 million token context window (128K max output), accepts text and image input with text output, and has a knowledge cutoff of June 2026. Adaptive thinking is always on, with five reasoning effort levels (low/medium/high/xhigh/max). Compared to the predecessor Fable 5, Fable 5.1 improves across agentic coding, long-horizon workflows, and knowledge work, with cache read pricing reduced 75% to $0.25/M tokens.
The iCreat platform offers this model via the endpoint https://api.icreat.ai/llm/anthropic/v1/messages (Anthropic Messages API compatible), at $2 per million input tokens, $10 per million output tokens, and $0.2 per million cached read tokens.
Model Positioning
Claude Fable 5.1 is positioned as Anthropic's most capable public model, designed for long-horizon agentic workflows, complex coding, and knowledge work.
The model is suited for multi-file migrations, architecture analysis, and cross-service debugging — scenarios where an agent must maintain a plan across many tool calls. Anthropic recommends starting most workloads with Opus 5 and escalating to Fable 5.1 when tasks demand stronger reasoning or sustained autonomous execution.
On the iCreat platform, the model is served through an Anthropic Messages API compatible endpoint at one-fifth of the official standard pricing.
Core Capabilities
Long-Horizon Agentic Workflows
Designed for repository-scale coding tasks, supporting multi-file migrations, architecture analysis, and cross-service debugging where an agent must maintain a plan across many tool calls.
1 Million Token Ultra-Long Context
Supports a 1,000,000 token context window with 128,000 token max output, enabling ingestion of entire codebases or complete document sets in a single request.
Multimodal Input
Accepts text and image input, supporting screenshot analysis, diagram understanding, scanned documents, and visual debugging workflows.
Adaptive Thinking
Adaptive thinking is always on, with the model automatically performing internal reasoning before generating responses. Five reasoning effort levels (low/medium/high/xhigh/max) provide flexible control.
Prompt Caching Optimization
Cache read pricing at only $0.2/M tokens (iCreat platform price) — one-tenth of the standard input rate, significantly reducing costs for repeated query scenarios.
Pricing
| Token Type | Unit Price | Unit |
|---|---|---|
| Input | $2 | per million tokens |
| Output | $10 | per million tokens |
| Cached Read | $0.2 | per million tokens |
| Cache Write | $2.5 | per million tokens |
Note: The above are iCreat platform prices. Anthropic's official standard pricing is $10 input, $50 output, $0.25 cache read, and $12.50 cache write per million tokens; iCreat's price is approximately one-fifth of the official rate. The iCreat platform price shall prevail.
Application Scenarios
- Long-horizon agentic coding workflows (multi-file migrations, architecture analysis, cross-service debugging)
- Complex research and large-scale document analysis
- Front-end and visual code generation
- Finance and analysis tasks
- Multimodal document understanding (screenshots, diagrams, scanned documents)
Model Comparison
Comparison Table 1: iCreat Pricing vs. Anthropic Official Standard Pricing
| Feature | iCreat Platform | Anthropic Official Standard |
|---|---|---|
| Input Price | $2/M tokens | $10/M tokens |
| Output Price | $10/M tokens | $50/M tokens |
| Cached Read | $0.2/M tokens | $0.25/M tokens |
| Cache Write | $2.5/M tokens | $12.50/M tokens |
| Endpoint | iCreat Anthropic-compatible | Anthropic official API |
| Model ID | claude-fable-5-1 | claude-fable-5-1 |
Note: iCreat pricing is approximately one-fifth of the official standard; model capabilities are identical. Anthropic also offers a Batch API (50% discount on standard rates).
Comparison Table 2: Anthropic Flagship Models
| Feature | Claude Fable 5.1 | Claude Opus 5 | Claude Fable 5 |
|---|---|---|---|
| Positioning | Most capable public model | Default flagship | Previous flagship |
| Release Date | 2026-09-01 | 2026 | 2026 |
| Context Window | 1M tokens | 1M tokens | 1M tokens |
| Max Output | 128K tokens | 128K tokens | 128K tokens |
| Input Price | iCreat $2 | Per platform | Per platform |
| Output Price | iCreat $10 | Per platform | Per platform |
| Cache Read (Official) | $0.25/M tokens | Per official | $1.00/M tokens |
| Adaptive Thinking | Always on | Supported | Supported |
Note: Fable 5.1 improves over Fable 5 in agentic coding and long-horizon workflows, with cache read pricing reduced 75%; Opus 5 is priced at half of Fable 5.1, and Anthropic recommends starting most workloads with Opus 5.
Why Choose Claude Fable 5.1?
- Anthropic's most capable public model, designed for long-horizon agentic workflows
- 1 million token ultra-long context for entire codebase ingestion
- Adaptive thinking always on with five reasoning effort levels
- Multimodal input supporting text and images for visual workflows
- iCreat platform pricing at one-fifth of the official standard
- Cache read at only $0.2/M tokens, extremely low cost for repeated queries
Specifications
| Field | Value |
|---|---|
| Model Name | Claude Fable 5.1 |
| Developer | Anthropic |
| Model ID | claude-fable-5-1 |
| Endpoint | https://api.icreat.ai/llm/anthropic/v1/messages |
| SDK base_url | https://api.icreat.ai/llm/anthropic |
| Release Date | 2026-09-01 |
| Model Type | Flagship LLM (Mythos class) |
| Authentication | Authorization: Bearer |
| Context Window | 1,000,000 tokens (1M) |
| Max Output | 128,000 tokens (128K) |
| Knowledge Cutoff | 2026-06 |
| Input Modalities | Text, Image |
| Output Modalities | Text |
| Adaptive Thinking | Always on, cannot be disabled |
| Reasoning Effort | low / medium / high / xhigh / max |
| Streaming | Supported |
| Function Calling | Supported |
| Structured Output | Supported |
| Prompt Caching | Supported (5-minute / 1-hour TTL) |
| Billing Unit | Per million tokens |
Architecture
The iCreat platform's Claude Fable 5.1 is served through an Anthropic Messages API compatible endpoint, allowing users to call it with the official Anthropic SDK or any compatible SDK. Requests must include the API Key in the Authorization header. The request body uses the Anthropic Messages format (model, max_tokens, system, messages fields). Adaptive thinking is always on and requires no manual activation; reasoning intensity is controlled via the effort parameter. The model supports streaming (stream: true), function calling, and prompt caching. Cache writes support 5-minute and 1-hour TTLs, with cache read pricing at one-tenth of the standard input rate.
Notes
- Adaptive thinking is always on; attempting to disable it or set an unsupported manual thinking budget returns a 400 error
- API Key should be passed via environment variables; avoid hardcoding it in source code
- iCreat platform pricing is approximately one-fifth of the official standard; model capabilities are identical
- Start with the default high effort, then test other reasoning effort levels after measuring quality and cost
- Cache read costs only $0.2/M tokens — one-tenth of the standard input rate, significantly reducing costs for repeated queries
- The model supports text output only; it cannot generate images
- Please safeguard your API Key and avoid hardcoding it in client-side code or public repositories
Frequently Asked Questions
What is the difference between iCreat pricing and Anthropic's official pricing?
iCreat platform pricing is approximately one-fifth of the official standard (input $2 vs $10, output $10 vs $50), with the same model ID and capabilities. Cache read on iCreat is $0.2 vs $0.25 on official. The iCreat platform price shall prevail.
Can adaptive thinking be turned off?
No. Adaptive thinking is always on — this is a design decision for Fable 5.1. Attempting to disable it or set an unsupported manual thinking budget returns a 400 error. Reasoning intensity can be controlled via the effort parameter (low/medium/high/xhigh/max), defaulting to high.
How do I choose reasoning effort?
Five levels: low (rapid response), medium, high (default), xhigh, and max (maximum reasoning). Higher levels produce deeper reasoning but with greater latency. Start with the default high, then test other levels after measuring quality and cost. At low or medium effort, Fable 5.1 achieves results comparable to or better than Fable 5 at lower cost.
Is streaming output supported?
Yes. Pass "stream": true in the request body to enable streaming. The model will return generated content token by token.
Is function calling supported?
Yes. The model is compatible with the Anthropic Tool Use protocol, and also supports structured output (JSON Schema), prompt caching, and computer use. Native web search is not supported (use external search tools via function calling).
Should I choose Fable 5.1 or Opus 5?
Anthropic recommends starting most workloads with Opus 5 (priced at half of Fable 5.1) and escalating to Fable 5.1 when tasks demand stronger reasoning, long-horizon autonomous execution, or large-scale code migrations. Fable 5.1 is for the hardest sustained work; Opus 5 is for most production scenarios.