It’s June 27, 2016. Scott Hanselman stands on a stage at Red Hat Summit, and for the first time in history, Microsoft isn't just talking about Windows. They’re running .NET on Red Hat Enterprise Linux. That moment marks the official .NET Core release date. It wasn't just a software update; it was a total culture shift.
Honestly, if you were around back then, the vibe was chaotic. Microsoft was the "Windows company," yet here they were, open-sourcing their crown jewels. Most people thought it was a fluke. It wasn't.
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Why the .NET Core release date changed everything
Before 2016, if you wanted to build with .NET, you were locked into the Windows ecosystem. Period. You needed Windows Server, IIS, and a healthy dose of patience for the monolithic .NET Framework. Then came .NET Core 1.0.
It was tiny. It was fast. It ran on a Mac.
The initial release was basically a "reboot" of the entire platform. Because it was rewritten from scratch, it didn't have all the features of the old framework. You couldn't just "copy-paste" your old code and expect it to work. That actually frustrated a lot of devs early on. But the trade-off was worth it: suddenly, we had a modular, high-performance runtime that could live in a Docker container without weighing 5 gigabytes.
The timeline: From Core 1.0 to the "Great Unification"
Microsoft didn't just stop at that June 2016 launch. They went on a tear. Looking back, the speed of releases was almost dizzying compared to the slow, multi-year cycles of the previous decade.
- .NET Core 1.0 (June 27, 2016): The big bang. Cross-platform, open-source, and admittedly a bit bare-bones.
- .NET Core 2.0 (August 14, 2017): This was the "I can actually use this now" version. It added over 20,000 APIs that were missing in 1.0, making it way easier to port old libraries.
- .NET Core 3.0 (September 23, 2019): A massive milestone because it brought support for Windows Desktop apps (WPF and WinForms) to the Core world.
- .NET Core 3.1 (December 3, 2019): The Long-Term Support (LTS) version that many enterprises still talk about with a certain fondness.
Then things got weird with the naming. Microsoft realized having ".NET Framework" and ".NET Core" as separate things was confusing everyone. So, they skipped version 4 (to avoid clashing with .NET Framework 4.8) and just called the next one .NET 5.
Basically, .NET 5 was the moment "Core" became just... .NET.
What most people get wrong about the release
There’s this common misconception that the .NET Core release date was the end of the old .NET Framework. It wasn't. Even now, in 2026, .NET Framework 4.8 is still supported as a component of the Windows OS. It’s the "undead" framework. It isn't getting new features, but it isn't going away either because half the world’s banking systems still run on it.
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Another thing? People forget how much the community actually built this. Unlike the old days, the development happened on GitHub. You could literally see the engineers arguing about performance in the pull requests. That transparency was probably more important than the code itself.
The performance leap was actually insane
You’ll hear people say .NET Core is "faster," but that’s an understatement. When they stripped out the legacy baggage, the benchmarks went through the roof.
TechEmpower benchmarks, which track web framework performance, saw ASP.NET Core jump from the bottom of the list to the top ten. We're talking about a framework that can handle millions of requests per second on a single machine. For a developer used to the "bloated" reputation of Microsoft tools, this was a massive "wait, really?" moment.
How to handle your legacy apps today
If you’re still sitting on a stack that hasn't moved since the .NET Core release date, you've got choices. You don't necessarily have to rewrite everything.
First, check your dependencies. Most modern NuGet packages support .NET Standard, which acts as a bridge between the old and the new. If your libraries support .NET Standard 2.0, you’re in a good spot.
Second, don't try to move the whole monolith at once. Use the "Strangler Fig" pattern. Build your new features in .NET 8 or .NET 9 (the current heavy hitters as of 2026) and slowly "strangle" the old app by routing traffic to the new services.
Third, look at the LTS (Long Term Support) schedule. Microsoft now releases a new version every November. Even-numbered versions (like .NET 6, 8, and 10) get three years of support. Odd numbers are "Standard Term" and only get 18 months. If you’re in a corporate environment, stick to the even numbers. It’ll save you a lot of headache.
Moving forward
The journey that started on June 27, 2016, has led us to a unified platform. Whether you’re building AI-driven microservices or simple web APIs, the "Core" DNA is what makes it work across Windows, Linux, and macOS.
Check your current project's target framework. If you're still on .NET Core 3.1 or .NET 5, those are long out of support. You should prioritize an upgrade to .NET 8 or .NET 10 to ensure you're getting the latest security patches and performance wins. Start by running the .NET Upgrade Assistant—it’s a surprisingly decent tool that handles much of the heavy lifting for you.
Once you've modernized, take a look at the native AOT (Ahead-of-Time) compilation features in the latest releases. It can slash your container startup times and memory footprint even further, making your cloud bills a lot more manageable.