GitHub Copilot adds Claude Fable 5.1 and Agent Merge

In its weekly changelog dated September 4, 2026, GitHub opened Claude Fable 5.1 to Copilot Pro+, Max, Business and Enterprise, started rolling Gemini 3.8 Flash out to the Pro tier as well, and made content exclusions generally available in the Copilot app and CLI. The roundup covers the week ending August 31.

The two model entries do not cover the same customers

Read the tier lists side by side and the difference matters. Claude Fable 5.1 appears for four tiers — Pro+, Max, Business and Enterprise. Gemini 3.8 Flash appears for five, adding the cheaper Pro tier.

So a solo developer on Copilot Pro gets the Google model in this round, not the new Anthropic one. GitHub also frames Gemini 3.8 Flash as a rollout in progress rather than a switch already flipped for everyone. No completion date is given.

Content exclusions reach general availability

The second item is about control rather than capability. Content exclusions — the rules an organization uses to keep specific paths and repositories out of what the assistant sees — are now honored by the Copilot app and the command line, and GitHub marks the capability generally available.

That closes the gap administrators complained about most: an exclusion rule that holds inside the editor but is ignored by the agentic tool running next to it protects very little. Whether enforcement behaves identically along every tool path is not spelled out in the entry.

VS Code 1.136: merge help and session hygiene

Four editor items come from VS Code 1.136. Agent Merge, flagged public preview, is meant to carry a pull request to a mergeable state by working through reviewer comments, failing checks and conflicts. Two more are labeled experimental: multi-root workspaces extend Copilot and Claude agent sessions across every folder in a workspace, and chat backgrounds allow built-in patterns or custom images.

The quietest item may be the one developers feel daily. Chat sessions are now grouped hierarchically, with the ones that need attention surfaced — which is exactly where running several agents at once currently falls apart.

The shorter entries

Four items appear without further detail. The JetBrains harness is generally available; enterprise settings accept any model as the default selection; Copilot code review can approve pull requests; and individual user budgets can carry expiration dates.

What this story does not establish

Exactly one independent source was available here: GitHub's own changelog post. That is vendor communication, not independent verification, and the claims above are reported as the vendor's claims.

Not verified, and therefore not asserted: pricing or premium-request consumption for the new models, regional availability, an end date for the Gemini rollout, and how well Agent Merge performs on real repositories. It also remains open whether Claude Fable 5.1 inside Copilot matches the model Anthropic offers directly.