Someone on IntelliJ 2025.1 who follows GitHub’s JetBrains install how-to is still sent to the Marketplace for version compatibility. That how-to (HTTP Date Sun, 11 Oct 2026 01:09:30 GMT, no last-modified) does not name 2025.1 or 2025.2.

Today’s changelog says GitHub Copilot has ended support for JetBrains IDE 2025.1. You now need 2025.2 or later to use the plugin.

Microsoft’s September 15 post (HTTP Date Sun, 11 Oct 2026 01:15:15 GMT, no last-modified) still says the plugin will discontinue 2025.1.x in the next few months, and that the existing plugin is expected to continue working. I fetched those pages; I did not run the plugin.