25–27 May 2021, online. This was the second all-virtual Build, three days of livestreams and on-demand sessions we watched from the office in Ibbenbüren rather than from a conference hall in Seattle. On paper it looked like a quiet one — no stadium, no big hardware moment, a lot of incremental Azure and tooling news. In hindsight it was anything but. One announcement on day one would turn out to be the first crack of light in what we now just call "the AI era," and most of the people watching it scrolled right past.
We want to be honest about that, because it's the most useful thing we can say about Build 2021 with the benefit of five years' distance: the headline of the conference was not the announcement that got the headlines. So let's walk through what actually happened, what we made of it at the time, and which threads turned out to matter.
GPT-3 shipped into a real product — and almost nobody noticed
The single most consequential thing at Build 2021 was buried inside a low-code demo. Microsoft announced that it was bringing GPT-3 — OpenAI's large language model — directly into Power Apps, as a feature that would let someone describe what they wanted in plain English and get back a working Power Fx formula. You could type "show me customers from the US whose subscription expired" and the tool would generate the formula and explain how it worked. The capability shipped under the name Power Apps Ideas.
Microsoft was explicit that this was a first. As the company put it, these were "the first product features powered by GPT-3" — not a research demo, not a lab teaser, but a feature heading into preview for real users. Charles Lamanna, then Microsoft's corporate vice president for the low-code application platform, framed the ambition plainly:
"Using an advanced AI model like this can help our low-code tools become even more widely available to an even bigger audience by truly becoming what we call no code."
And he put a number on it that, in May 2021, sounded almost absurd:
"In all cases, there is a human in the loop. This isn't at all about replacing developers, it's about finding the next 100 million developers in the world."
Read that quote again with what you now know. A year and a half later GitHub Copilot was general; four years later "agents" was the entire theme of the conference. The "human in the loop" framing, the insistence that this augments rather than replaces, the dream of pulling a hundred million more people into building software — all of it was there, on a Power Platform slide, in the spring of 2021. The vocabulary that would dominate every keynote for the rest of the decade got its first real outing here, and it got it in a tool aimed at business users rather than at us.
We'll be straight about our own reaction at the time: we were interested but not electrified. Natural-language-to-Power-Fx looked like a clever convenience for citizen developers, not a foundation for the kind of production software we build. We were wrong about the scope — we read it as a Power Platform feature when it was actually a statement of company direction. We were right, though, to file away the underlying fact: Microsoft and OpenAI had moved from "interesting partnership" to "this is going into shipping products." That fact was the one worth tracking, and it's the thread that, years later, would let us build production AI features into customer software on infrastructure we could actually reason about.
A clarification we owe ourselves, because the earlier version of this post blurred it: what shipped at Build 2021 was GPT-3 in Power Apps, not a general-purpose Azure OpenAI service. The broad, developer-facing Azure OpenAI offering came later. At Build 2021 the news was narrower and, honestly, more interesting for being narrow — Microsoft chose to introduce the world's most talked-about language model not through an API for AI specialists, but through a low-code tool for everyone. That choice told you exactly where the company thought this was going.
.NET 6 Preview 4: Hot Reload, MAUI, and the unification finally landing
For a shop like ours that lives in C# and .NET all day, the substantial news was .NET 6 Preview 4, which dropped the same day, 25 May. This was the preview where the long-promised "One .NET" story stopped being a roadmap slide and started being something you could install.
The headline developer-experience feature was Hot Reload — the ability to edit your running app's source and see the change without restarting or hitting a breakpoint. Microsoft's own description was refreshingly plain:
"Hot Reload is a new experience that enables you to make edits to your app's source code while it is running without needing to manually pause the app or hit a breakpoint."
If you have never lost twenty minutes of a debugging session to "change one line, rebuild, click back through five screens to get to the broken state, repeat," that sentence will not move you. If you have — and we have, thousands of times — it reads like a small act of mercy. Hot Reload would later become the centre of a genuinely awkward open-source controversy in the autumn of 2021, but at Build it was simply a very welcome productivity win.
The rest of Preview 4 was the unification finally cohering:
- .NET MAUI — the evolution of Xamarin.Forms into a single framework for building native Windows, macOS, iOS and Android apps from one codebase — landed in Visual Studio.
- Blazor hybrid apps, letting you build cross-platform desktop and web UI with web technology while still reaching native device capabilities.
- Minimal APIs and smaller, faster container images for the cloud-native crowd — the start of the "tiny microservice in a handful of lines" style that .NET 6 would ship.
- Quality-of-life additions we still reach for: single-file publishing with compression, the new DateOnly and TimeOnly types, and serious FileStream performance work on Windows.
Microsoft made a point we appreciated: platform unification was, in their words, "baked into everything we do" rather than being its own headline feature. After years of "is it .NET Framework, .NET Core, Mono, or Xamarin?" confusion, the most valuable thing about .NET 6 was that the question was finally going away.
A 64-bit Visual Studio, just over the horizon
The other tooling story belongs in any honest account of this season, with one caveat: Visual Studio 2022 was actually announced a few weeks before Build, on 19 April 2021, not on the Build stage itself. We're flagging that because the original short version of this post implied the VS 2022 roadmap dropped during Build week, and it didn't — it dropped in the same spring, in the same breath of news, but separately.
The substance, though, was real and it mattered to us: VS 2022 would be the first 64-bit Visual Studio, finally freeing the IDE from the 4 GB memory ceiling that anyone working on a large solution had been quietly fighting for years. Microsoft promised the first public preview "this summer"; it duly arrived in mid-June 2021. Hot Reload from .NET 6, a 64-bit IDE that could actually hold a big codebase in memory, and the MAUI tooling — taken together, this was the most credible reset of our day-to-day environment in a long time.
Azure and data: the unglamorous shipping news
Underneath the AI and tooling stories, Build 2021 did the steady Azure-and-data work that tends to land in customer projects first. The ones we noted:
- Azure Cosmos DB serverless went generally available across all APIs — consumption-based pricing for spiky or unpredictable workloads, which is exactly the shape of a lot of the line-of-business apps we ship.
- Azure SQL Database ledger entered preview, bringing cryptographic, tamper-evident verification to a relational database — aimed squarely at healthcare and finance, where "prove this record wasn't altered" is a real requirement and not a nice-to-have.
- Azure Logic Apps Standard brought a new single-tenant hosting model with better performance and proper local development in Visual Studio Code — a meaningful upgrade for the integration plumbing that quietly holds enterprises together.
- On the AI-infrastructure side, Azure Machine Learning managed endpoints went to preview and PyTorch Enterprise on Azure launched — both signals of Microsoft building out the serious, production end of its AI stack while the GPT-3 demo grabbed attention at the other end.
One useful correction while we're being careful: Azure Container Apps, the serverless-container service we were excited about, was not a Build 2021 announcement — that came later, at Ignite in November 2021. And Azure Static Web Apps reached general availability earlier that same month (12 May), just ahead of Build rather than during it. We had originally lumped Container Apps into the Build list; it doesn't belong there, and we'd rather fix the record than let a tidy-but-wrong bullet stand.
Teams as a developer platform
Microsoft also spent real energy at Build 2021 turning Teams from a chat app into a development surface. The relevant pieces: Fluid components arriving in Teams chat (in private preview), Together mode extensibility and shared stage integration for meeting apps, meeting event APIs, and a proper Developer Portal for Teams to manage and publish apps.
This was directly useful to the kind of internal-tooling work we do for customers — when the whole company already lives in Teams all day, the cheapest place to put a custom tool is right inside the app they never close. (For the record: Microsoft Mesh, the "meetings in the metaverse" idea that often gets attached to this era, was an Ignite announcement from March 2021, not Build — and Mesh-for-Teams specifically came at Ignite that November. We mention it only to keep the timeline honest.)
On the Windows side, the developer story was Project Reunion 0.8 in preview and WinUI 3 reaching general availability with WebView2 support — the slow, important work of unifying the Win32 and UWP worlds into a single modern app model. Worthy, if not exactly thrilling.
"The next generation of Windows"
And then there was the tease. In his keynote, Satya Nadella did something he rarely does — he pre-announced an announcement:
"I've been self-hosting it over the past several months, and I'm incredibly excited about the next generation of Windows."
He went on, in the same breath, to make it a developer pitch:
"Our promise to you is this: We will create more opportunity for every Windows developer today and welcome every creator who is looking for the most innovative, new, open platform to build and distribute and monetize applications."
The whole industry correctly read this as a Windows 11 trail. The actual unveiling came five weeks later, on 24 June 2021. The interesting part, in retrospect, is how he framed it — not as a UI refresh but as an economic-opportunity pitch to developers, with "open platform" and "monetize applications" doing the heavy lifting. That was a shot at the app-store debate raging at the time, and a preview of the more developer-friendly Microsoft Store that shipped with Windows 11. A tease, yes — but a pointed one.
Why it mattered for us
Here is the candid summary, written with five years of hindsight we didn't have in the room.
Build 2021 looked minor and turned out to be a hinge. The GPT-3-in-Power-Apps announcement was the first time Microsoft put a large language model inside a shipping product, and the language it used to do so — human in the loop, the next 100 million developers, augment not replace — became the script for the entire AI decade that followed. We under-rated it. We read it as a low-code curiosity when it was a declaration of where the whole company was heading. The lesson we took, and still hold, is to watch where a vendor first ships a risky new capability, not just that they ship it: Microsoft chose to debut GPT-3 in a tool for non-developers, and that single choice told you more about its ambitions than any benchmark could.
The more immediately practical wins were the ones we acted on the same week. Hot Reload and the prospect of a 64-bit Visual Studio materially improved our daily work. The .NET 6 unification meant we could stop apologising for the runtime's fragmented past and start betting on a single, coherent platform — a bet that has paid off every year since. And Cosmos DB serverless and Azure SQL ledger were the kind of unglamorous, production-grade building blocks that quietly end up under real customer systems.
None of it changed our north star: ship software that has to work the first time, for industries where a bug isn't a CSS regression but a missed export or a failed payment. Build 2021 just stocked the toolbox — and, though we didn't fully see it at the time, fired the starting gun on the change that has shaped everything we've built since.
"Microsoft loves developers." — Nadella's signature framing, as true in 2021 as it remains today.
Sources & further reading
- Microsoft Source — From conversation to code: Microsoft introduces its first product features powered by GPT-3 (25 May 2021): https://news.microsoft.com/source/features/ai/from-conversation-to-code-microsoft-introduces-its-first-product-features-powered-by-gpt-3/
- Microsoft — Build 2021 Book of News: https://news.microsoft.com/build-2021-book-of-news/
- .NET Blog — Announcing .NET 6 Preview 4 (25 May 2021): https://devblogs.microsoft.com/dotnet/announcing-net-6-preview-4/
- Visual Studio Blog — Visual Studio 2022 (19 April 2021): https://devblogs.microsoft.com/visualstudio/visual-studio-2022/
- Visual Studio Magazine — Visual Studio 2022: Faster, Leaner and 64-bit (19 April 2021): https://visualstudiomagazine.com/articles/2021/04/19/vs-2022.aspx
- CNBC — Microsoft CEO Satya Nadella teases big Windows update at Build (25 May 2021): https://www.cnbc.com/2021/05/25/microsoft-build-nadella-teases-windows-update-teams-azure-improved.html
- InfoQ — Microsoft Releases Azure Static Web Apps into General Availability (May 2021): https://www.infoq.com/news/2021/05/azure-static-web-apps-ga/
- TechCrunch — Microsoft launches Azure Container Apps (2 November 2021, for the corrected timeline): https://techcrunch.com/2021/11/02/microsoft-launches-azure-container-apps-a-new-serverless-container-service/
Where this post corrects its own earlier, shorter version — the scope of the GPT-3 news, the timing of Visual Studio 2022, and the fact that Azure Container Apps belongs to Ignite 2021 rather than Build — the corrections are deliberate and sourced above.
Image credits
All photos are used under their respective Creative Commons licences; we are grateful to the photographers.
- New Workspace — © simon_music, CC BY-SA 2.0, via Flickr (source).
- Democratizing Deep Learning with Nervana and Google Brain — © jurvetson, CC BY 2.0, via Flickr (source).
- Screen-python-code-matplotlib-physics-simulation — © MikeRun, CC BY-SA 4.0, via Wikimedia Commons (source).