Two Launches, Four Days Apart
Fable 5.1 targets long-running work, financial analysis, and front-end visual coding, according to Microsoft's admin documentation. Astra showed up almost everywhere else on the same day it launched: Copilot Cowork, Copilot Studio, GitHub Copilot, Microsoft Foundry. Charles Lamanna, who runs Copilot at Microsoft, said Astra lets people hand off bigger tasks instead of chopping them into small steps.
Admins pick which model their users get. The setting lives in the Microsoft 365 admin centre, and it can be scoped down to a single team if needed. A few months ago this was a preference. Now it decides your bill and which compliance regime kicks in.
The Fine Print Doesn't Match
GitHub Copilot Business and Enterprise customers get Astra by default. Someone has to go turn it off. Microsoft's documentation doesn't specify the same default-on setting for Fable 5.1, but there's a bigger wrinkle buried there regardless. Because it's still a preview model, Anthropic may handle the data behind it as an independent processor, not as a Microsoft subprocessor. Those two statuses carry different legal weight. A compliance team that's already reviewed Microsoft's standard Anthropic subprocessor terms hasn't necessarily reviewed this.
There's also a gap most admins won't notice until it bites them. Flipping on Anthropic as a subprocessor does nothing to extend Purview's data-loss prevention or audit logging to Claude traffic. Someone has to configure that separately, by hand.
Where the Money Came From
This didn't start in September. Microsoft agreed in November 2025 to put up to $5 billion into Anthropic. Nvidia went further, pledging up to $10 billion. The deal pushed Anthropic's valuation to somewhere around $350 billion. Anthropic agreed to buy $30 billion of Azure compute in return and kept an option open for another gigawatt of capacity built on Nvidia's Grace Blackwell and Vera Rubin chips.
Foundry customers see Claude charges land right on their Azure invoice, same as everything else they're running there. A number of them can even offset it against Azure Consumption Commitments signed long before Claude showed up as an option. Copilot Cowork doesn't work that way at all. Anthropic's models there run on Copilot Credits, an add-on charge stacked onto whatever seat price a customer already pays. Azure never enters the picture.
Anthropic officially became a Microsoft subprocessor on 6 January 2026. Most regions have Claude switched on by default now. The EU, the UK, and EFTA countries are the exception, admins there still have to opt in manually.
The Open Question
Purview wasn't built for this. It tracks files sitting on a server, not what an AI model can piece together from permission-approved sources it's allowed to see. Every new model that joins Copilot, with its own separate data terms, makes that blind spot bigger. The real question for Anthropic's enterprise customers isn't whether Fable 5.1 works well. It's whether the model's current data processor status is a preview-only footnote or whether it's what Claude's terms inside Copilot will look like once the preview label comes off.