Cowork now has three gears, not one
Anthropic has published guidance on when to reach for Claude Fable 5 inside Claude Cowork, and it's a useful moment for any Australian business running, or considering, a Cowork setup to revisit how they're using it. Cowork doesn't default to Fable 5. The standard model is Claude Sonnet 5, which is the right call for the quick, everyday tasks most people run through Cowork day to day. Claude Opus 4.8 suits deep work where you already know what the finished result should look like. Fable 5 is reserved for the most complex, ambiguous jobs: the ones that used to be out of reach because earlier models lost the thread over a long, multi-step run.
That distinction matters commercially, not just technically. Fable 5 spends more time thinking and draws down more of a workspace's usage allowance per task, so treating it as the default for routine work is an expensive habit rather than a productivity one. Most of the Cowork setups we scope for Sydney and Melbourne businesses start with exactly this problem: a team picked the biggest model out of caution, then wondered why their monthly allowance ran out by the third week.
Where Fable 5 earns its keep
Fable 5 is built to carry long, asynchronous work with less supervision. Folding a week of research into a first-draft memo. Running due diligence ahead of a board pack. Working through a folder of contracts and redlining each one against a standard template. In Anthropic's own example, a Fable 5 run building next year's budget from this year's actuals caught and corrected its own misread run rate mid-task, rather than letting that error compound through every projection that followed.
For a mid-sized Australian firm, that self-correction is the difference between a Cowork run you have to babysit and one you can hand off properly. It matters even more when the underlying data is sensitive: a due-diligence file that has to hold up under the Privacy Act, or a board pack for an APRA-regulated lender, is exactly the kind of job where a model that checks its own work earns the extra thinking time.
Use Sonnet 5, the default, for same-day tasks: drafting an email, summarising a document, pulling a quick report
Move to Opus 4.8 when the shape of the output is clear but the work is substantial: a detailed report, a structured analysis, a first-pass code review
Reserve Fable 5 for jobs with real ambiguity or a multi-day arc, and where getting it wrong is costly: due diligence, financial modelling, or a client-facing deliverable
The effort dial most teams never touch
Model choice is only half the decision. Fable 5 also ships with an effort setting, and it behaves differently depending on which way you turn it.
Higher effort: Fable 5 plans more before starting and checks in more as it runs, suited to complex, multi-step projects you want completed end to end without a human re-reading every step
Lower effort: trades some of that supervision for speed, and Anthropic notes it still often matches or beats earlier models running at their highest setting
In practice, most Cowork users never touch this dial because they never needed to reach for Fable 5 in the first place. That's fine for a solo operator. It's a gap worth closing once a team is running Cowork across multiple people and functions, because the effort setting is one of the few levers that trades speed for thoroughness without changing which model you're paying for.
What it costs to get the default wrong
There are two ways teams get this wrong, and they sit at opposite ends of the same mistake. The first is defaulting everything to Fable 5 to be safe, which burns through a monthly usage allowance fast and leaves a team paying for depth they didn't need on a task that was always going to be a five-minute email draft. The second is never touching Fable 5 at all, so every ambiguous, multi-day job still gets run through Sonnet 5 with someone checking in every few minutes to correct it, which defeats the point of automating the work in the first place.
We help Australian teams work out which model and effort setting actually fits each workflow inside their Cowork setup, part of the scoping we do on every AU$3,500 Cowork setup engagement. Getting the routing right up front, rather than letting each person in the business guess, is usually worth more than the setup fee inside the first month of usage.
One safeguard worth knowing about
Fable 5 also ships with new classifiers that catch potential misuse in cybersecurity or biology and chemistry-related requests. When one triggers, Claude Opus 4.8 quietly takes over that response and tells you it happened. Anthropic has tuned these conservatively, which means some entirely harmless Cowork requests that brush against those topics get redirected too. Worth knowing in advance, so it reads as a safeguard doing its job rather than a fault when your team hits it.
If your team is running everything through the default and wondering why results are inconsistent, or why the usage allowance never lasts the month, that's usually the first thing worth fixing. Book a brainstorm and we'll map your actual workflows to the right model before you scale Cowork across the business.
