GitHub Copilot switches GPT-6 Astra on by itself and leaves Claude Fable 5.1 off

Two frontier models reached general availability in GitHub Copilot three days apart, and an administrator who decides nothing ends up with one of them and not the other. GPT-6 Astra arrived on September 4, 2026, and Claude Fable 5.1 on September 1. Both are limited to Copilot Pro+, Max, Business, and Enterprise, and both appear in the same ten places, from Visual Studio Code to Eclipse.

Astra arrives switched on

GitHub describes GPT-6 Astra as a model for long-horizon, autonomous coding and agentic tasks, one that plans, validates, and confirms its own results before it treats a task as finished. That is the vendor's description of its own model. No benchmark figure accompanies the announcement, and no premium request multiplier is given.

The sentence that matters to whoever manages the seats is about defaults. Enterprise and Business administrators control the model through the model policy in Copilot settings, and GitHub states that under default model enablement new models are enabled automatically unless an administrator has turned off the global default or explicitly disables the model. An organization that has never touched that global setting now has Astra in its model picker without having chosen it.

Fable 5.1 arrives switched off, and it keeps the prompts

Claude Fable 5.1 reached the same four plans on September 1, 2026, and the same ten surfaces. Its policy behaves the other way around. GitHub states plainly that the policy is off by default and that an administrator has to enable it in Copilot settings before anyone on a Business or Enterprise plan can select the model.

The reason is data handling. Unlike the other Claude models in Copilot, Fable 5.1 requires data retention by default: Anthropic retains data, including prompts and outputs, to operate the safety classifiers that detect harmful use. Eligible customers can use Fable 5.1 and Fable 5 with zero data retention through the end of the calendar year, under a time-bound exemption that lasts while Anthropic rolls out Enterprise Frontier Safeguards. GitHub names that program without describing what it will require afterwards.

• Both models are limited to Copilot Pro+, Max, Business, and Enterprise. Neither reaches the plain Pro plan.
• Both are selectable in Visual Studio Code, Visual Studio, Copilot CLI, the Copilot coding agent, the Copilot app, github.com, GitHub Mobile on iOS and Android, JetBrains IDEs, Xcode, and Eclipse.
• The Copilot harness became generally available in Copilot for JetBrains, which GitHub says delivers features faster and improves code quality.
• Neither announcement states a premium request multiplier, so the two models cannot yet be compared on cost per request.

What an administrator has to open this week

The two defaults pull in opposite directions, and that is worth a look at the model policy page even in an organization that has decided nothing. One model can appear without a decision. The other cannot appear without one. A team that reads its own silence as caution gets the opposite of what it intended in at least one of the two cases.

The retention exemption has a date on it, and it is the end of the calendar year rather than a contract anniversary. Any enterprise workflow built on Fable 5.1 before then runs under a temporary arrangement whose replacement, Enterprise Frontier Safeguards, is named but not described. Teams whose own agreements forbid prompt retention should treat that as the deadline it is, and check whether they are on the eligible list before they enable the policy.