The GitHub Copilot Chat client for VS Code is now open source under the MIT license. Here's the source code:
"As Copilot Chat releases in lockstep with VS Code due to its deep UI integration, every new version of Copilot Chat is only compatible with the latest and newest release of VS Code. This means that if you are using an older version of VS Code, you will not be able to use the latest Copilot Chat.
Only the latest Copilot Chat versions will use the latest models provided by the Copilot service, as even minor model upgrades require prompt changes and fixes in the extension. An older version of Copilot Chat will still use the latest version of Copilot completions."
