Claude Fable 5
Claude Fable 5 is Anthropic's most capable widely released model, built for the most demanding reasoning and long-horizon agentic work. Claude Fable 5 runs long, complex, and asynchronous tasks with fewer check-ins and is available on AI Gateway via Anthropic, Bedrock, Google Vertex AI with adaptive thinking and configurable effort.
View API reference- Input and output price
- Prices from: Input $10, Output $50, Per 1M tokens
- 24h uptime
- Loading AI Gateway uptime
import { streamText } from 'ai'
const result = streamText({ model: 'anthropic/claude-fable-5', prompt: 'Why is the sky blue?'})Copy link to headingPlayground
Try out Claude Fable 5 by Anthropic. Usage is billed to your team at API rates. Free users (those who haven't made a payment) get $5 of credits every 30 days.
Claude Fable 5
Claude Fable 5
Copy link to headingProviders
Route requests across multiple providers. Copy a provider slug to set your preference. Visit the docs for more info. Using a provider means you agree to their terms, listed under Legal.
| Provider |
|---|
Copy link to headingUptime24 hours
Direct request success rate on AI Gateway and per-provider. Visit the docs for more info.
Copy link to headingThroughput24 hours
P50 throughput on live AI Gateway traffic, in tokens per second (TPS). Visit the docs for more info.
Copy link to headingLatency24 hours
P50 time to first token (TTFT) on live AI Gateway traffic, in milliseconds. View the docs for more info.
Getting started
Call Claude Fable 5 through AI Gateway with the AI SDK generateText and streamText functions, or through the OpenAI Chat Completions, OpenAI Responses, and Anthropic Messages APIs by changing the base URL. AI Gateway authenticates the request and routes it to an available provider.
Install the AI SDK (pnpm add ai dotenv), create an API key from the API Keys page, and set it as AI_GATEWAY_API_KEY in your environment. Full setup is covered in the text generation quickstart.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'anthropic/claude-fable-5', prompt: 'Why is the sky blue?', });
console.log(result.text);}
main().catch(console.error);Top-level parameters
The same Claude Fable 5 request in each API format AI Gateway supports.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'anthropic/claude-fable-5', system: 'You are a concise technical assistant.', prompt: 'Summarize the tradeoffs between static generation and SSR.', maxOutputTokens: 1024, });
console.log(result.text);}
main().catch(console.error);Standard parameters like prompt, messages, temperature, and tools work as documented in the AI SDK docs. These are the parameters with model-specific behavior.
| Parameter | Type | Required | Description |
|---|---|---|---|
model | string | Yes | Model ID in the form creator/model, e.g. anthropic/claude-fable-5. AI Gateway routes the request to an available provider. |
maxOutputTokens | number | No | Hard cap on generated tokens. Claude Fable 5 supports up to 128,000 output tokens. Reasoning tokens count toward this limit. |
reasoning | 'provider-default' | 'none' | 'minimal' | 'low' | 'medium' | 'high' | 'xhigh' | No | Provider-agnostic reasoning effort, available in AI SDK 7 or later. Maps to the provider’s native reasoning configuration; reasoning settings under providerOptions take precedence when both are set. See the Reasoning section below. |
providerOptions | Record<string, JSONValue> | No | AI Gateway routing options under gateway, plus any provider-native options under the provider’s own namespace — see the table below. |
Input limits
| Input | Formats | Sources | Max count | Max size | Limits |
|---|---|---|---|---|---|
| Text | — | — | — | — | Prompt and response share the 1M-token context window |
| Image | — | URL, base64, Uint8Array | — | — | Sent as image parts in messages; counts as input tokens |
| — | URL, base64, Uint8Array | — | — | Sent as file parts in messages; counts as input tokens |
Provider options
Set AI Gateway routing options under providerOptions.gateway. For provider-specific options, pass them under the provider’s namespace as documented by the AI SDK.
Learn more in the AI SDK anthropic provider docs.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'anthropic/claude-fable-5', prompt: 'Why is the sky blue?', providerOptions: { gateway: { only: ['anthropic', 'bedrock'], }, }, });
console.log(result.text);}
main().catch(console.error);These AI Gateway routing options apply to every model. Provider-specific options pass through under the provider’s own namespace (for example providerOptions.anthropic) exactly as documented by the AI SDK.
| Parameter | Type | Required | Description |
|---|---|---|---|
providerOptions.gateway.only | string[] | No | Restrict routing to these provider slugs. Requests fail over only within the listed providers. |
providerOptions.gateway.order | string[] | No | Preferred provider order. Listed providers are tried first; unlisted providers remain available as fallbacks. |
providerOptions.gateway.sort | 'cost' | 'ttft' | 'tps' | No | Rank candidate providers by price, time to first token, or tokens per second instead of the default routing order. |
providerOptions.gateway.zeroDataRetention | boolean | No | Route only to providers with a zero-data-retention policy for this model. |
Routing across providers
AI Gateway serves the same model through multiple providers and fails over automatically. order expresses a preference while keeping every provider eligible; only is a hard allowlist — if none of the listed providers are available the request fails instead of falling back.
Options under a provider's own namespace (for example providerOptions.anthropic) are forwarded to that provider with the request. Providers ignore option namespaces that don't apply to them, so it is safe to set provider options alongside gateway routing options.
Reasoning
AI Gateway bridges reasoning across every API format. The AI SDK exposes a provider-agnostic top-level reasoning level (none, minimal, low, medium, high, or xhigh); the Chat Completions and Responses formats take the same effort under reasoning.effort; and the Anthropic Messages format uses a native thinking token budget. Whichever you send, the gateway maps it to the target model’s native configuration, converting between effort levels and token budgets as needed. Reasoning-related settings under providerOptions take full precedence over the top-level reasoning value and are never merged. Reasoning tokens typically count toward your output-token usage, though how they’re reported and billed varies by provider.
Learn more in the AI Gateway reasoning guide.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'anthropic/claude-fable-5', prompt: 'Explain the Monty Hall problem step by step.', reasoning: 'high', });
console.log(result.text);}
main().catch(console.error);Image input
Send images alongside text as message parts. Images count as input tokens.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'anthropic/claude-fable-5', messages: [ { role: 'user', content: [ { type: 'text', text: 'Describe this image.' }, { type: 'image', image: 'https://example.com/photo.jpg' }, ], }, ], });
console.log(result.text);}
main().catch(console.error);PDF input
Attach PDFs as file parts. Their contents count as input tokens.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'anthropic/claude-fable-5', messages: [ { role: 'user', content: [ { type: 'text', text: 'Summarize this document.' }, { type: 'file', mediaType: 'application/pdf', data: 'https://example.com/document.pdf', }, ], }, ], });
console.log(result.text);}
main().catch(console.error);Tool calling
Expose tools the model can call. Define each tool’s inputs with a Zod schema.
import { generateText, tool } from 'ai';import { z } from 'zod';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'anthropic/claude-fable-5', prompt: 'What is the weather in San Francisco?', tools: { getWeather: tool({ description: 'Get the current weather for a location', inputSchema: z.object({ location: z.string() }), execute: async ({ location }) => ({ location, temperatureC: 18 }), }), }, });
console.log(result.text);}
main().catch(console.error);Copy link to headingMore models by Anthropic
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|---|
| 1M | 1.4 s | 83 tps | $5/M+1 more | $25/M+1 more | Read$0.50/M Write$6.25/M | $10/K | +3 |  +1 | 07/24/2026 | |||||
| 1M | 1.5 s | 116 tps | $2/M | $10/M | Read$0.20/M Write$2.50/M | $10/K | +3 | +1 | 06/29/2026 | |||||
| 1M | 1.1 s | 104 tps | $5/M+1 more | $25/M+1 more | Read$0.50/M Write$6.25/M | $10/K | +3 | +1 | 05/28/2026 | |||||
| 1M | 0.8 s | 74 tps | $3/M | $15/M | Read$0.30/M Write$3.75/M | $10/K | +3 | +1 | 02/17/2026 | |||||
| 1M | 1.2 s | 53 tps | $5/M+1 more | $25/M+1 more | Read$0.50/M Write$6.25/M | $10/K | +3 |  | 02/05/2026 | |||||
| 200K | 0.5 s | 115 tps | $1/M | $5/M | Read$0.10/M Write$1.25/M | $10/K | +3 | +1 | 10/15/2025 |
Copy link to headingAbout Claude Fable 5
Claude Fable 5 became available on AI Gateway on July 1, 2026. Access was briefly suspended under US export controls and restored in July 2026 once the controls were lifted; the restored model is the same model, with updated and more robust safety classifiers. Anthropic describes Claude Fable 5 as a Mythos-class model made safe for general availability, with capabilities that exceed any model Anthropic had widely released before. The launch materials report leading results across nearly every benchmark Anthropic tested, spanning software engineering, knowledge work, vision, and scientific research.
Long-horizon agentic work is the design target. Claude Fable 5 handles long-running, complex, and asynchronous tasks where previous models needed more frequent check-ins. At launch, Claude Fable 5 supports the memory tool, code execution, programmatic tool calling, compaction, tool result clearing through context editing, and vision input, plus task budgets in beta. Those are the building blocks for agents that run for hours without losing state.
Adaptive thinking is always on. Claude Fable 5 decides when and how deeply to reason, and thinking: { type: 'disabled' } is not supported. Use the effort parameter to control thinking depth and cost per request. Raw chain of thought is never returned: set thinking.display to summarized for a readable summary, or keep the default omitted.
Safety classifiers ship as part of Claude Fable 5 and can decline certain requests, including occasional false positives on routine tasks such as coding and debugging. A refusal returns stop_reason: "refusal" as a successful response, not an error, and reports which classifier declined. Configure fallback models through the models array in providerOptions.gateway so AI Gateway retries refused requests on the next Claude model in your list, such as Claude Opus 4.8 or Claude Sonnet 5. Fallbacks work on every API format.
Through AI Gateway, Claude Fable 5 is available with the standard unified API, observability, retries, and failover across Anthropic, Bedrock, Google Vertex AI. Set the model to anthropic/claude-fable-5 in the AI SDK, Chat Completions API, Responses API, Messages API, or other API formats, from TypeScript or Python. AI Gateway mirrors provider pricing with no markup and adds no platform fee on inference, including for Bring Your Own Key requests.
Copy link to headingWhat To Consider When Choosing a Provider
- Configuration: Claude Fable 5 includes safety classifiers that can decline certain requests, and even routine tasks such as coding and debugging can occasionally trigger them. A declined request returns
stop_reason: "refusal"as a successful response rather than an error. Configure fallback models withproviderOptions.gateway.modelsso AI Gateway retries refused requests on the next model in your list, such as Claude Opus 4.8 or Claude Sonnet 5. Fallbacks work on every API format, and AI Gateway observability tracks refusals. - Configuration: Adaptive thinking is the only thinking mode on Claude Fable 5. Use the
effortparameter to control reasoning depth and cost. Premium per-token rates reward routing: send the hardest work to Claude Fable 5 and keep high-volume simple traffic on a cheaper Claude tier. - Zero Data Retention: Zero Data Retention is offered on a per-provider and model basis. See the documentation for details.
- Authentication: AI Gateway authenticates requests using an API key or OIDC token. You do not need to manage provider credentials directly.
Copy link to headingWhen to Use Claude Fable 5
Best for
- Long-Horizon Agentic Work: Long-running, complex, and asynchronous tasks that previously needed more frequent check-ins
- Demanding Reasoning Problems: Hard software engineering, knowledge work, and scientific research where output quality justifies premium compute
- Large-Context Workloads: A context window of 1M tokens and up to 128K tokens output tokens cover big codebases and long agent histories
- Stateful Autonomous Agents: Memory, compaction, code execution, and programmatic tool calling keep multi-hour sessions on track
- Production Agent Infrastructure: Workflows that benefit from AI Gateway routing across Anthropic, Bedrock, Google Vertex AI with retries and failover
Consider alternatives when
- Cost-Sensitive Production Traffic: Claude Sonnet 5 delivers strong agentic performance at a much lower per-token price
- Latency-Critical Interactive Use: A Haiku-tier model is faster and cheaper for well-bounded, high-throughput requests
- Simpler Response Handling: Sonnet-tier models don't include Fable-specific safety classifiers, which keeps refusal handling out of your integration
Copy link to headingConclusion
Claude Fable 5 makes Mythos-class capability generally available with safeguards in place. Use Claude Fable 5 for the hardest reasoning problems and for agent pipelines that run long, complex, and asynchronous tasks with minimal supervision. Route high-volume or latency-sensitive traffic to a cheaper Claude tier and reserve Claude Fable 5 for work that needs the ceiling.
Copy link to headingFrequently Asked Questions
What is Claude Fable 5 built for?
Claude Fable 5 is Anthropic's most capable widely released model, built for the most demanding reasoning and long-horizon agentic work. Claude Fable 5 handles long-running, complex, and asynchronous tasks where previous models needed more frequent check-ins.
How does thinking work on Claude Fable 5?
Adaptive thinking is the only thinking mode, and Claude Fable 5 decides how deeply to reason per request. Control depth and cost with the
effortparameter. Raw chain of thought is never returned; setthinking.displaytosummarizedfor a readable summary.What happens when Claude Fable 5 declines a request?
The response returns
stop_reason: "refusal"as a successful response, not an error, and reports which classifier declined. Configure fallback models withproviderOptions.gateway.modelsand AI Gateway retries the request on the next model in your list, such as Claude Opus 4.8 or Claude Sonnet 5, on every API format.What agent tooling does Claude Fable 5 support?
At launch, Claude Fable 5 supports the memory tool, code execution, programmatic tool calling, compaction, tool result clearing through context editing, and vision input. Effort control ships as standard, and task budgets are available in beta.
What context window and output limit does Claude Fable 5 have?
Claude Fable 5 has a context window of 1M tokens and supports up to 128K tokens output tokens per request, enough for large codebases, long document sets, and extended agent histories.
Does AI Gateway support Zero Data Retention for Claude Fable 5?
Zero Data Retention is not currently available for this model. Anthropic does not offer Zero Data Retention for Claude Fable 5 because some misuse patterns are only visible across cumulative requests. Prompts and completions are retained for 30 days and are not used to train Claude. Zero Data Retention is offered on a per-provider basis. See https://vercel.com/docs/ai-gateway/capabilities/zdr for details.
What is the pricing for Claude Fable 5?
AI Gateway mirrors provider pricing with no markup and adds no platform fee on inference. Rates are listed on this page and shift when providers update their pricing.
How do I call Claude Fable 5 through AI Gateway?
Set the model to
anthropic/claude-fable-5in the AI SDK, Chat Completions API, Responses API, Messages API, or other API formats, from TypeScript or Python. AI Gateway handles authentication, retries, and failover acrossanthropic,bedrock,vertex.
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