Upgrade Sitefinity without assuming 15.4 is modern .NET

13.3 LTS — the last Web Forms home — retired in April 2026. Current 15.4 LTS is still .NET Framework 4.8. We will tell you whether to climb the CMS, rebuild the front end, or leave Sitefinity.

Book a free 30-minute discovery callTalk through your Sitefinity site

Australian .NET team. We look at the site before anyone talks about a rebuild.

Still running Sitefinity?

The site still works. That is why it has been left alone.

Progress Sitefinity is a packaged .NET CMS. A lot of the installs we hear about were built on Web Forms or older MVC, then left on 13.x or early 15 because the pages still rendered. Then a lifecycle date, or a Cloud conversation, made the version impossible to ignore.

You might recognise one of these:

  • You stayed on 13.3 LTS because it was the last Web Forms version
  • Custom widgets, modules, or Feather / MVC templates are the front end
  • You are on 15.0–15.3 and thought “we are on 15” was enough
  • Someone said upgrade to latest and you would be off Framework
  • Sitefinity Cloud will not take the version you have
  • You are not sure whether to stay on Sitefinity or leave it

You do not need a new brand, or a DXP pitch. You need a clear read on the CMS and the front end you already have.

Why these sites stall

Sitefinity is still a real product. Current official release is Sitefinity 15.4 (LTS), GA November 2025. Progress is moving 15.4 LTS onto a product-update model rather than new official minors. The problem is rarely “Sitefinity vanished”. It is that an upgrade to latest does not exit Framework unless you also move the frontend off Web Forms / old MVC.

13.3 retired

Web Forms

Still Framework

Custom widgets

13.3 LTS retired in April 2026. The site does not switch off.

Progress phases are Active, Sunset, Retired. Retired means no obligation to ship product updates; security is not assured. 13.3 LTS (GA March 2021, last officially supported Web Forms version) retired April 2026. Sites keep running. Updates stop. Retired versions are not supported in Sitefinity Cloud.

Caption under the diagram:

Version climb is one project. A Web Forms frontend is another. That is why sites stall.

Web Forms gets no security fixes after 13.3 — including on 14 and 15.

Progress discontinued the Web Forms frontend in 14.1. Beyond 13.3, Web Forms gets no support, no features, no bug fixes, including security updates. Recommended alternatives are ASP.NET Core or Next.js. MVC can still run; the vendor recommends modernising it too. A shop that stayed on 13.3 because it was the last Web Forms LTS is now on a retired CMS, and Web Forms is unsupported on every later version as well.

15.4 is still .NET Framework 4.8.

Official system requirements for 15.4: Framework 4.8, ASP.NET MVC 5, IIS 10+. Decoupled front ends — an ASP.NET Core Renderer on .NET SDK 10, or Next.js — are optional. Owners who wanted off Framework are disappointed after a successful CMS upgrade. Only the optional renderer is modern .NET.

The rest of the 15 line is already on a short clock.

15.0–15.3 retire November 2026. 14.4 LTS entered Sunset in April 2026 and retires April 2027. Vendor upgrade-path advice: retired versions, and 13.3, should go to 14.4 LTS or 15.4 LTS (they prefer latest). 14.4 / 15.x should plan 15.4 LTS. A 2025 “we are on 15” shop that is not on 15.4 may already be weeks from Retired.

Frontend modernisation is a rebuild.

Custom widgets, modules, and Feather / MVC templates do not become Core or Next.js widgets. Progress’s Migration Analyzer is a scoping tool, not a converter. Licence and maintenance gate product updates: current Subscription or Maintenance and Support is required. Cloud will not host a retired version — upgrade first, then Cloud.

None of that makes the content, media, or URLs worthless. It does mean “NuGet-upgrade on Monday and we are on modern .NET” is the wrong first move.

How we work

We start with the install, not with a destination.

1

Look at what you have

Version (13.3, 14.x, 15.0–15.3, or 15.4), Web Forms or MVC, custom widgets and modules, licence / maintenance status, and how the site is hosted. We will tell you what a CMS climb will actually change, and what the frontend still has to rebuild.

2

Decide the job

There are three honest outcomes. We recommend one, not all three.

3

Do the work in stages

Content, media, and URLs matter more than a clean-room rebuild. Redirects and the pages people actually use come across. Unused widgets do not.

4

Hand it back so the next person can run it

Source, a short record of what changed, and a site someone else can understand.

Three honest outcomes

  • Upgrade to Sitefinity 15.4 LTS and keep MVC for now if you are already committed to Sitefinity. Vendor allows that. They still recommend modernising the frontend. Adding the ASP.NET Core Renderer or Next.js, or moving to Sitefinity Cloud after a supported version, is the same family — still a frontend project if you are on Web Forms.
  • Leave Sitefinity for another CMS or a headless plus custom front when the frontend rewrite is the whole job anyway.
  • Stabilise first when the site is fragile: document the widgets and modules, confirm what the licence actually covers, and plan the real move without taking production down to guess.

We will not tell you Sitefinity is finished. 15.4 LTS is a current product, supported no earlier than January 2030 on the lifecycle page. We will not tell you it is modern .NET, and we will not tell you WordPress is the answer to every Sitefinity site. If you already know you want to stay on Sitefinity forever, a dedicated Progress partner may be a better fit. If you want an honest fork in the road, talk to us.

What we need for the first call

A URL and a rough version is enough to start.

  • Which Sitefinity version (13.3, 14.x, 15.0–15.3, 15.4)
  • Whether the frontend is Web Forms, MVC, or already decoupled
  • Which custom widgets, modules, and templates are still used
  • Licence / maintenance status, if you know it (we do not need the key on the call)
  • Whether Cloud is on the table, or you must stay self-hosted
  • Hosting today (old Windows server, Azure, someone else’s box)
  • What “done” looks like: stay on Sitefinity, leave it, or get a clear picture first

The first call is 30 minutes. You leave with a recommendation you can take to a manager, not a rebuild estimate pulled from thin air.

Related work

We have taken over and modernised ageing .NET systems for Australian organisations, including work with Data#3, Hastie, NESS, and NSW Health. Hastie was SharePoint 2007 plus ASP.NET 3.5. NSW Health TESL was SharePoint plus ASP.NET 4.0. NESS is nopCommerce and Dynamics NAV. That is related Microsoft web work, not a published Sitefinity case study. A 13.3 or 15.x install still starts with its own assessment. We will not pretend it is a project we have already published.

FAQ

Does upgrading to 15.4 get us off .NET Framework?
No. The CMS itself stays on Framework 4.8 / MVC 5 / IIS. Only the optional ASP.NET Core Renderer or a Next.js front leaves Framework.
Can we keep Web Forms if we stay on 13.3?
13.3 was the last supported Web Forms version, and it retired in April 2026. After 13.3, Web Forms gets no security fixes on 14 or 15 either. The frontend is a rebuild if you want a supported path.
Will the site switch off on Retired day?
No. Progress says sites run; updates stop. Retired versions also cannot go to Sitefinity Cloud.
Do we have to stay on Sitefinity?
No. 15.4 LTS is a real product. Leaving only makes sense when the frontend rewrite is the whole job, or the custom modules will not come with you.
We only have a backup and an old server.
That is common. Bring that.

Talk through the Sitefinity site you already have

Thirty minutes. Bring a URL and a version number if you know it. We will tell you whether to climb to 15.4, rebuild the front end, leave Sitefinity, or leave it alone for now — and we will not pretend 15.4 is modern .NET.

Book a free 30-minute discovery call