Claude Fable 5 is Anthropic’s most capable generally available model, built for long-running, complex and asynchronous work. Claude Fable 5 is particularly effective carrying out multi-step workflows (such as conducting deep research that it incorporates in a first-draft memo, performing due diligence before generating board presentations, or going through a folder to redline multiple contracts, to name a few) on its own for extended periods of time, testing and evaluating its results as it goes.
Maximizing the model’s capabilities requires a change in how you work with it. As models improve over time, we’ve refined our recommendations for getting more out of Claude, including prompting best practices, providing context, and building skills that capture repeatable processes like weekly team updates, sales call prep, or customer feedback analysis. Those practices still matter with Claude Fable 5, in fact, the model performs even better with them in place.
Claude Fable 5 applies your context, preferences, and skills across entire tasks, even those that take days to complete, while previous models may have lost track over long stretches and needed reminding. Working with it resembles working with a highly capable colleague: you explain the situation, agree on what a strong final result looks like, and let your colleague work. Less of your time goes to checking each step, so more of it can go to deciding what the work should be.
Our prompting guide for Claude Fable 5 provides a detailed list of capability improvements and recommended behavior and prompting changes. In this article, we cover how some of those apply to Claude Cowork, Anthropic’s agentic AI system for knowledge work.
How Claude Fable 5 complements Claude Cowork
Claude Cowork is built for creating finished work. Give it an objective, and it manages the rest, even when the task is large and complex. A big job gets broken into parts that run at the same time, each with its own subagent, a separate instance of Claude that takes one part of the job to complete and reports back. That is how Claude gets through large amounts of information quickly. Claude also manages large tasks by setting a plan at the start, and it can check its own results against it as it goes.
Claude Fable 5 has a wide lead over our other models on long, complex tasks and Claude Cowork tasks are often exactly that, with dozens of steps, each building on the last. Take a project like building next year’s budget based on this year’s actuals. Claude gets access to and reads the spreadsheets, pulls the run rates, projects each line, reconciles the projections against targets, and writes the summary. If it misreads a run rate early, the error will flow into each projection after it. Claude Fable 5 plans the workflow before starting and checks results as it goes, so it can catch the misread number while the job runs and correct it.
Decide when to use Claude Fable 5
Claude Fable 5 isn’t the default model in Claude Cowork; you need to select it. As of the time of publication, the default is Claude Sonnet 5, and it is the right choice for everyday tasks you yourself would handle in quick passes. Claude Opus is a dependable choice for deep work with a clear shape, where you know what the end result looks like. Claude Fable 5 is for the projects that feel the most complex or ambiguous, and may have been out of reach for prior models. It spends more time thinking and more of your usage limits, but that may be worth it on work that’s time-consuming or costly to get wrong. We recommend that you reserve Claude Fable 5 for your most important work, especially jobs that use multiple tools and require a series of judgment calls.
You can further tune your choice with Claude’s effort setting. At higher effort, Claude Fable 5 plans more before it kicks off a job and checks in more throughout its run. Keep effort higher for complex or multi-step projects you expect Claude to complete from beginning to end. At lower effort, you’ll get a faster response, while still taking advantage of Claude Fable 5 intelligence. Consider using it for tasks that still need frontier judgement, but not deep explorations, such as agentic runs made of many easy steps or work where the result is easy for Claude to check. In our testing, Claude Fable 5 at lower effort often matched or exceeded the performance of earlier models at their highest effort levels. For a more detailed look under the hood, we explain how model choice and effort interact in Claude Code.
It’s also worth noting that Claude Fable 5 comes with a new set of classifiers: separate AI systems that detect potential misuse in requests related to cybersecurity or to biology and chemistry. When they trigger, the response is automatically handled by Claude Opus 4.8 instead, and users are informed whenever this occurs. Opus 4.8 is a highly capable model in its own right, and the chat stays on Opus from there; start a new one to get back to Claude Fable 5. We tuned these safeguards conservatively so we could release a Mythos-class model for general use both safely and quickly, so they’ll sometimes catch harmless requests, including phrases in Claude Cowork that only touch on related topics. We’re working to reduce these false positives as we refine the safeguards.
Start with as little as an idea
When you kick off a task, you don’t always know what you’re trying to accomplish. That early stretch is where Claude Fable 5 can be a powerful thought partner, and in Claude Cowork it works from your skills, tools, and knowledge.
For example, if you see a news announcement relevant to your industry or company, you can ask Claude: “Here’s the announcement, tell me what changes for us, considering everything you know about my organization.” You read the output and as you start to develop a strategy, Claude builds a plan to produce the assets that you need, starting in the same conversation in Claude Cowork where the brainstorming happened.
Brainstorming in Claude Cowork gives the model your real material to think with: it can read the files you’ve shared and use the tools you’ve connected while you talk, so it can offer relevant suggestions. It notices gaps in an idea while the idea is still easy to change, and it shows you directions you hadn’t considered. And when the task begins in the same conversation, Claude Fable 5 already carries the goal you settled on, the constraints you named, and the decisions you made along the way.
For example, a data scientist at Anthropic came to Claude Cowork with an idea for a new analytics dashboard while the team was still figuring out what it should show. Because Claude Fable 5 could read the team’s usage data during the conversation, it knew which problems take weeks to get noticed, and it ranked the metrics that would have caught them sooner. By the end of the conversation, the data scientist had a shortlist of metrics worth adding and a clickable prototype.
Here are two prompts that can help you evolve your idea into an output:
- Ask Claude to interview you: “Before you start, ask me everything you need to know to get this right.”
- Ask for directions: “Here is roughly what I want. Give me three ways you could take it, with a quick sample of each.”
