For millions of QGIS users, 4.0 is the biggest version jump since the 2.x-to-3.x transition — and unlike a feature release, this one is fundamentally about plumbing. The project announced the move to Qt6 in April 2025 [1], and after the schedule slipped from October 2025 to February 2026 to give plugin developers and packagers more time [2], the new era is now underway.
Why the migration had to happen
The forcing function was upstream: Qt 5.15 — the GUI framework beneath every QGIS window — entered extended, commercial-only support in May 2025, meaning free security updates on Qt5 ended [2]. Staying put was quietly becoming a security decision, not just a technical-debt one.
The timeline that matters for production shops
- QGIS 3.44 is the final 3.x release and the last 3.x long-term release [2].
- QGIS 3.40 LTR was extended by four months, until May 2026, to smooth the gap [2].
- The first 4.x LTR will be QGIS 4.2, landing in LTR repositories in October 2026 [2].
Translation: if your organization tracks LTR — as most production deployments should — your real migration window is now through October 2026, when 4.2 becomes the supported baseline.
The plugin question
Here is the reassuring part: 4.0 deliberately retains deprecated APIs, so most plugins need only minimal changes [1]. The project has been explicit that this is a modernization release, not a feature release — the goal is a clean foundation on Qt6, not a rewrite of your workflow. Practical advice: inventory the plugins your work actually depends on, check each for a 4.x-compatible release before you switch your main machines, and keep a 3.40 LTR install around until your whole toolchain is proven on 4.x.