We never officially had a written version support policy on major Certbot versions, and with our more frequent major release schedule we had to make it clear how long we could or even should support previous major releases.
After discussion we dropped full support for previous major versions in favor of discretionary back-ports at the team's behest of only the previous major version. For comfort and context, we have rarely had to do back-ports up to this point.
For more clarity or further explanation, you can read the architectural (or in this case policy) decision record here: Architectural Decision Records 2025 · certbot/certbot Wiki · GitHub)
Below is the current support matrix for visual understanding:
| Major Version | Support Level |
|---|---|
| >= 4.0 | Full Support |
| 3.x | Discretionary Backports |
| <=2.x | None |