How to Use Claude Fable 5

Claude Fable 5 is a model in the Claude lineup, available through supported Claude plans and through the Anthropic API. Using it is straightforward once you know which plan or API access includes it: you select it from the model menu in Claude, or set it as the active model in Claude Code. The steps below walk through both paths.

Your project context — the task state, the rules you work by and where things stand — does not change when you switch models. Tools like fenbs keep that record outside any one model, so switching from an earlier Claude model to Fable 5 does not mean re-explaining the project from scratch.

Check whether your plan includes Fable 5

Not all Claude plans include every model. Before selecting Fable 5, confirm that your subscription or API access includes it. Open the Anthropic pricing page↗ (opens in a new tab) or your API dashboard and look for Fable 5 in the list of available models.

If Fable 5 does not appear in your model selector on claude.ai, it is likely not included in your current plan. In the API, a model not available on your plan will return an error rather than silently falling back to another model.

For the Fable 5 context window size and how it compares to other Claude models, see the fable-5-context-window guide. For prompts optimized for Fable 5 tasks, see the prompts-for-fable-5 guide.

Select Fable 5 in claude.ai

In the Claude web app, open a new conversation or an existing one. Look for the model selector near the compose area or at the top of the conversation. It typically shows the current model name. Click it and choose Fable 5 from the list of models your plan includes.

The model you select applies to the current conversation. If you start a new conversation, Claude may default to a different model. Check the selector at the start of each session if you need Fable 5 specifically.

In Claude Projects, you can set a default model for the project. Open the project settings and look for a model option. If your plan includes Fable 5, setting it there means every new conversation in the project starts with that model selected.

Select Fable 5 in Claude Code

Claude Code uses the model configured for your API key or subscription. To select Fable 5, set the ANTHROPIC_MODEL environment variable before starting a session:

export ANTHROPIC_MODEL=claude-fable-5-latest
claude

Replace claude-fable-5-latest with the exact model ID shown in the Anthropic API documentation↗ (opens in a new tab). Model IDs are versioned; use the ID Anthropic lists as current rather than guessing the format.

If you use a .env file in your project, you can add the ANTHROPIC_MODEL line there so the model is set automatically each time you open the project. Claude Code reads .env files in the project directory if configured to do so.

Use Fable 5 through the Anthropic API

If you access Claude through the API in your own code, pass the Fable 5 model ID in the model field of your request. The format is the same as for any other Claude model:

{
  "model": "claude-fable-5-latest",
  "max_tokens": 1024,
  "messages": [{ "role": "user", "content": "Your prompt here" }]
}

Use the exact model ID from the Anthropic API documentation↗ (opens in a new tab) rather than a guessed string. An incorrect model ID returns an error; there is no silent fallback to a different model.

What to save before switching models

When you switch to Fable 5 mid-project, the model starts with no memory of earlier sessions. Before switching, save where the task stands: what was completed, what was checked, what remains, and any decisions made during the session.

A fenbs Where we left off note is the practical way to do this. At the end of the session on the previous model, ask it to save progress to fenbs. At the start of the Fable 5 session, ask it to read the project context from fenbs. It gets the current state without you retyping everything, and the Decisions and rules appear first.

How to do this with fenbs

1. Create a free account and add your project to fenbs.
2. Write the task description, Decisions and rules (the instructions that apply to this project), and a Where we left off note covering the current state.
3. Connect Claude to fenbs over MCP from Integrations. The same connection works across Claude models including Fable 5.
4. At the start of each Fable 5 session, ask Claude to read the project context from fenbs. It gets the Rules, task state and Where we left off before you give the first prompt.
5. Before the session ends, ask Claude to save its progress so the next session — on any model — starts from the current state.

For the general Claude setup and what to expect from the web app, see what is Claude AI. For the Claude API and how it handles model selection, see claude-api.

Model versions in the API are typically available for a period after a newer version releases, so switching to Fable 5 does not immediately invalidate existing integrations. Check the Anthropic model deprecation page for timelines if you have a production system still on an older model.