github-copilot

Since August 21, 2026 mentioning @GitHub in Slack starts a Copilot cloud agent session the whole channel can steer. Here is the setup, the Slack Code channel model, why the pull request comes from an app identity instead of you, what the thread context capture actually exposes, and how the two separate billing meters add up.

GitHub's September 1, 2026 changelog lets Copilot submit an approving review that satisfies a repository's required-approval rule. It is off by default, scoped by file globs, and dismissed on new commits. Here is what actually changes in your branch protection.

Instructions files are deterministic and always sent. AGENTS.md sits at the bottom of the documented repository precedence list. Copilot Memory is a separate store Copilot writes for itself, read by only three surfaces, and it is not in the precedence list at all. Here is the support matrix and the rule for deciding where each convention belongs.

The experimental /rubber-duck command in VS Code 1.135 hands the agent's plan, code, and tests to a model from another family for review. GPT-5.4 critiques Claude, and the cross-family choice is the whole point.

Agent Plugins 1.0.0 standardizes exactly two component types: skills and MCP servers. Slash commands, hooks, subagents, rules, LSP servers, permission config and secrets all stay vendor-specific. Here is the field-by-field matrix across Claude Code, Cursor, Copilot and Codex, and which layout to author in.

GitHub's August 27 and August 28, 2026 changelogs remove the 20,000 line review cap, start reviewing bot-authored PRs, and flip the default review effort from Lite to Balanced on September 28. All three push AI credit consumption up in the same month.

A server that vanished from /mcp with no error is almost always an allowlist. Run claude mcp add on the same server: the add path prints the reason the load path swallows.

Since August 3, 2026 you can pick a reasoning level next to the model when you start a Copilot cloud agent task. The Agent Tasks REST API has no equivalent parameter, so scripted dispatch cannot set it. Here is where the control exists, which levels each model exposes, what lands on the wire, and how to pin a default instead.

Claude Code and GitHub Copilot both ship allowedMcpServers and deniedMcpServers, but the matchers behave differently. serverName is a fallback that a single serverCommand entry silently disables, deny is a union while allow is not, and an invalid allowlist locks everything out.

GitHub's August 6, 2026 changelog adds allowedMcpServers and deniedMcpServers to copilot/managed-settings.json. URL and argv matchers, deny-wins precedence, and a fail-closed default the older name-based registry never had.