Anthropic has unveiled Claude Fable 5, its most capable general‑availability model to date. What is more Microsoft has already moved to bring it into Microsoft 365 Copilot as an opt in preview model choice. It’s rolling out now but must be enabled before you can use it…
This is another clear signal that Copilot is becoming a true multi‑model AI platform, giving organisations more choice and more capability as work becomes increasingly complex and multi‑step.
What Is Fable 5 and Why Is It Different?
Fable 5 is Anthropic’s new Mythos‑class model. This uses the same underlying model as Mythos 5, but with additional safeguards that make it suitable for broad enterprise use.
Where previous Claude models like Opus excelled at deep reasoning, writing, and analysis, Fable is actually designed for:
- Long‑running, multi‑day tasks
- Deep research and multi‑stage workflows
- Large‑scale coding projects and migrations,
- Vision‑based reasoning across documents, diagrams, and UI screenshots
- Autonomous agent‑style work with self‑checking and planning
Anthropic describes Fable as the model for “your most ambitious work” – the kind of tasks that older models simply couldn’t sustain. Interesting
Why Microsoft Is Bringing Fable Into Microsoft 365 Copilot
Microsoft’s announcement mirrors Anthropic’s (naturally) messaging and frames Fable as a model designed for longer, multi‑step workflows – exactly the kind of work Copilot is increasingly being used for.
As business move beyond simple prompts and if pronation retrieval into doing stuff, Copilot is now helping users to:
- Plan multi‑stage tasks
- Draft and iterate across documents
- Analyse work content
- Connect insights across meetings, files, chats, and business data
This is all powered by Work IQ, Microsoft’s grounding layer that ensures Copilot responses are tied to your actual work context and enables it to perform at the fastest possible speeds.
It will roll out (once enabled) to
- Microsoft 365 Copilot – model selector
- Copilot Studio – for building agents
- Microsoft Foundry – enterprise agent development
- Researcher agent – deep, multi‑step research tasks
Adding Fable gives Copilot users a new model choice that is purpose‑built for deep, contextual, multi‑step work.
Important Considerations before enabling Fable 5
Fable 5 is available as an opt in preview.
Microsoft highlights one key factor that regulated and risk sensive organisation need to be aware of.
(Currently) using Claude Fable 5 (preview) involves 30‑day data retention by Anthropic for safety monitoring.
As such Microsoft suggests that IT Admins review Anthropic’s retention requirements. This is necessary to enable to models which is done via the Copilot pane in the M365 admin centre.
Organisations can also decide (when enabled) whether to enable Fable 5 for no one, some or all users.
Final Thoughts
Microsoft continues to add more model choice inside Microsoft 365 Copilot, ensuring their customers have the fastest choice and access to the latest frontier models without having to subscribe to multiple different AI tools.
With this choice, Enterprise protections stay in place, IT stay in control of which models are enabled.
Copilot is becoming an AI orchestration layer, not a single‑model assistant. I’m also excited to see Microsoft own AI models hopefully start to make an appearance in M365 Copilot next month.
Links for further reading.
Anthropic news https://www.anthropic.com/news/claude-fable-5-mythos-5
Microsoft announcement:
https://techcommunity.microsoft.com/blog/microsoft365copilotblog/available-today-anthropic-claude-fable-5-in-microsoft-365-copilot/4526832
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