Claude Fable 5 — deep reasoning, with forced tool calls
Claude Fable 5 keeps working for teams already built on it, including forced tool use. $8.00 / 1M input, $40.00 / 1M output per 1M tokens.
- Adaptive thinking
- 1M-token context
- Images and PDFs
- Prompt caching
- Streaming
Try Claude Fable 5
Chat with Claude Fable 5, attach images or PDFs, and see the tokens and cost of every answer.
claude-fable-5$8.00 in · $40.00 out per 1M tokens
Try one of these prompts
Messages are billed from your balance at the rates below, like an API call. Failed requests are free.
Real Claude Fable 5 output
One prompt, sent to Claude Fable 5 at low effort. Unedited.
Explain the difference between optimistic and pessimistic locking in a database, in two short paragraphs, and say when to use each.
Optimistic locking assumes conflicts are rare. Transactions read data without locking it, and when they try to write, the system checks whether the data changed since it was read (typically via a version number or timestamp). If it did change, the update is rejected and the application must retry. Pessimistic locking assumes conflicts are likely: a transaction locks the data as soon as it reads it, blocking other transactions from modifying (or sometimes even reading) it until the lock is released. Use optimistic locking when contention is low—such as web applications where many users read data but rarely update the same records—since it avoids the overhead and blocking of locks and scales better. Use pessimistic locking when contention is high or the cost of a failed retry is expensive—such as financial transactions or inventory systems where multiple processes frequently update the same rows—since holding a lock guarantees the update will succeed without conflicts.
Generated 2026-09-27. Answers vary from run to run.
Claude Fable 5 pricing
Claude Fable 5 is billed per token from your balance. Rates below are live, the same ones your account is charged.
Example sizes are for illustration. Your bill follows the tokens each request reports.
| Item | Counted as | Rate | Billing |
|---|---|---|---|
| Input | Prompt tokens not read from cache | $8.00 / 1M | Per 1M tokens |
| Output | Answer and thinking tokens | $40.00 / 1M | Per 1M tokens |
| Cache read | Prompt tokens served from the prompt cache | $0.80 / 1M | Per 1M tokens |
| Cache write, 5 minutes | Tokens written to a 5-minute cache | $10.00 / 1M | Per 1M tokens |
| Cache write, 1 hour | Tokens written to a 1-hour cache | $16.00 / 1M | Per 1M tokens |
| Failed request | Any request that returns an error | Free | Not charged |
What is Claude Fable 5?
Claude Fable 5 is Anthropic's previous Fable model for demanding reasoning, still available alongside Claude Fable 5.1. It reads up to 1M tokens, writes up to 128K per request and thinks adaptively at the effort you set.
Claude Fable 5 accepts forced tool use through tool_choice, which Claude Fable 5.1 does not. If your pipeline depends on that, or on answers you have already tested, Claude Fable 5 lets you keep it running unchanged.
Model ID: claude-fable-5 · Input: text, images, PDFs · Output: text · Formats: Anthropic Messages, OpenAI Chat Completions, OpenAI Responses.
Two ways to use Claude Fable 5
Call it from your code, or let your coding agent do it for you.
Call it from your backend
Point the official Anthropic SDK at SeedRouter and keep your code. Claude Fable 5 also answers the OpenAI formats.
- 1Create an API key
- 2Set the base URL to https://api.seedrouter.ai
- 3Send claude-fable-5 as the model
Hand it to your coding agent
Copy a ready prompt. Your agent shows the request and cost before anything is spent.
- 1Copy the prompt
- 2Paste it into your agent
- 3Approve the request
What Claude Fable 5 is good at
Claude Fable 5 is a steady choice when your workflow is already tuned to it.
Deep reasoning
Claude Fable 5 handles problems that need many careful steps.
Forced tool calls
Require a specific tool with tool_choice. Claude Fable 5 still supports it.
Tested behavior
Keep prompts and evaluations you built on Claude Fable 5 as they are.
1M-token context
Long codebases, contracts and transcripts fit in one request.
Images and PDFs
Claude Fable 5 reads charts, screenshots and documents with your text.
Effort you control
Low effort for simple steps, max for the hard ones.
What teams build with Claude Fable 5
Structured pipelines
Force a tool call on every step so each output lands in your schema.
Existing agents
Run agents built and evaluated on Claude Fable 5 without retuning.
Careful analysis
Review contracts, code or data where mistakes are expensive.
Start using Claude Fable 5 in four steps
- 01
Create a key
Sign in and create an API key. Add credit whenever you need it; there is no subscription.
- 02
Change the base URL
Point the Anthropic or OpenAI SDK at https://api.seedrouter.ai. Your code stays the same.
- 03
Pick Claude Fable 5
Send claude-fable-5 as the model. Set effort to trade depth for speed and cost.
- 04
Check the bill
Every request shows its tokens and charge in your usage records.
Claude Fable 5 on SeedRouter at a glance
What you can use today.
| Feature | Claude Fable 5 |
|---|---|
| Anthropic Messages API | Yes, official format |
| OpenAI Chat Completions | Yes |
| OpenAI Responses | Yes |
| Image and PDF input | Yes, by URL or base64 |
| Prompt caching | 5-minute and 1-hour |
| Forced tool use | Yes |
| Failed requests | Not charged |
Batch processing and fast mode are not offered.
Claude Fable 5 limits
1M-token context
On Claude Fable 5, prompt, files and history share one 1M-token window.
128K tokens out
One Claude Fable 5 request can return up to 128K tokens, thinking included.
Thinking stays on
Adaptive thinking cannot be turned off. Lower the effort to make it think less.
Sampling settings
Claude Fable 5 follows the official notes on temperature, top_p and top_k; test before relying on them.
Why call Claude Fable 5 through SeedRouter
One key, three formats
Call Claude Fable 5 with Anthropic Messages, OpenAI Chat Completions or Responses, all with the same key.
Pay per token
Top up once and spend it on any model. No plan, no monthly fee.
Failures are free
A request that errors is not charged.
Live prices
The rates on this page are the rates your account pays.
Prompt caching
Mark long, reused context and later Claude Fable 5 requests read it at the cache rate.
Images and PDFs
Send charts, screenshots and documents with your prompt.
Streaming
Stream Claude Fable 5 tokens as they arrive with stream: true.
Related models
Other models you can call with the same key.
Call Claude Fable 5.1 with the Anthropic or OpenAI SDK. Deep reasoning, 1M-token context, cheap cached reads, live pricing and a playground to try it today.
View pricingCall Claude Opus 5.5 with the Anthropic or OpenAI SDK. 1M-token context, adaptive thinking, live per-token pricing and a playground you can try right now.
View pricingClaude Fable 5 guides
Walkthroughs and comparisons for this model.
Claude Fable 5.1, Fable 5 and Opus 5.5 API pricing per million tokens: input, output and prompt-cache rates, how a request is billed, and API vs Claude plans.
Call the Claude Fable 5.1 API: get an API key, use the claude-fable-5-1 model ID, send a first request in Python or Node.js, and switch to Opus 5.5.
Run Claude Fable 5.1, Fable 5 or Opus 5.5 in Claude Code with a SeedRouter API key: the environment variables, model selection, and what each session costs.
Claude Fable 5.1 vs Fable 5 vs Opus 5.5 compared: specs, prices, official benchmark scores, what changed from Fable 5 and Opus 5, and which model to pick.
Is Claude Fable 5 still available? Why it was suspended on June 12, 2026, when it came back, its status today, and how to call it through the API right now.
Is Claude Fable 5 free? What the Claude Free, Pro and Max plans include, whether a free Fable 5 API key exists, and how to test it with free sign-up credit.
Claude Fable 5 FAQ
What is Claude Fable 5?+
Claude Fable 5 is Anthropic's Fable model for demanding reasoning, released June 9, 2026. It has a 1M-token context window, writes up to 128K tokens per request and thinks adaptively at the effort you set.
Is Claude Fable 5 still available?+
Yes. Anthropic lists Claude Fable 5 as active (legacy) and suggests moving to Claude Fable 5.1 for better performance. You can keep calling Claude Fable 5 through SeedRouter.
What is the Claude Fable 5 model ID and how do I call it?+
The model ID is claude-fable-5. Create a SeedRouter API key, point the Anthropic SDK at https://api.seedrouter.ai and send claude-fable-5 as the model; the request and response keep the official Messages format.
How much does Claude Fable 5 cost?+
Claude Fable 5 is billed per token: $8.00 / 1M for input and $40.00 / 1M for output per 1M tokens, plus lower rates for prompt-cache reads and writes. A request that fails is not charged.
What is the difference between Claude Fable 5 and Claude Mythos 5?+
Anthropic offers Claude Mythos 5 separately, by invitation only, for defensive cybersecurity work. It shares Claude Fable 5's specifications. Claude Fable 5 is the model open to everyone.
What effort levels does Claude Fable 5 support?+
Claude Fable 5 accepts low, medium, high, xhigh and max, with high as the default. Thinking stays on; effort decides how much of it you pay for.
What is the Claude Fable 5 knowledge cutoff?+
Anthropic gives January 2026 as the reliable knowledge cutoff for Claude Fable 5. Claude Fable 5.1 and Claude Opus 5.5 go up to June 2026.
Can Claude Fable 5 generate images?+
No. Claude Fable 5 reads text, images and PDFs, but it only writes text. For pictures, use an image model with the same SeedRouter key.
Should I move from Claude Fable 5 to Claude Fable 5.1?+
Claude Fable 5.1 costs the same per input and output token, reads cache at a quarter of the cost and is stronger on long tasks. Stay on Claude Fable 5 if you rely on forced tool use, which Claude Fable 5.1 does not support.
Keep Claude Fable 5 running
Send a Claude Fable 5 request from the playground or your own code in minutes.