Upgrade to .NET 10 LTS: What Teams Must Do Now

.NET 10 LTS landed on November 11, 2025, with three years of support through November 2028. If you run web backends, client apps, or services on .NET today, this is a high‑leverage upgrade window. The headline isn’t just performance; it’s safer defaults, clearer language features in C# 14, ASP.NET Core 10 identity improvements like passkeys, and solid runtime+JIT work that adds up in production. This guide explains what changed, what breaks, and how to ship .NET 10 LTS this quarter without blowing up your roadmap.

Why .NET 10 LTS matters right now

Three reasons: support, speed, and security. As an LTS release, .NET 10 receives fixes through mid‑November 2028. That gives you breathing room to standardize on one runtime across services. It’s also the fastest general‑purpose .NET so far—thanks to JIT de‑abstraction (better devirtualization and inlining), improved code layout, and new hardware acceleration paths like AVX10.2 on the right silicon. On the security front, recent HTTP request smuggling fixes in Kestrel highlighted how quickly web stacks can move; landing on the LTS trains you on patched, maintained builds.

There’s one practical constraint: to target the new net10.0 TFM, use the latest toolchain. The 10.0 SDK loads fine on recent Visual Studio, but targeting net10.0 specifically requires Visual Studio 2026 (version 18.x) or newer. If you’re on VS 17.14, you can build older TFMs but won’t be able to target .NET 10 directly. Plan your IDE rollout with the runtime.

What’s new for web backends: ASP.NET Core 10

ASP.NET Core 10 is a quality‑of‑life release for teams that live in production. The most visible addition is first‑class passkey support (WebAuthn/FIDO2) in ASP.NET Core Identity—with out‑of‑the‑box UI baked into the Blazor Web App template. If you’ve been waiting for a passwordless default that users actually accept, this is it. It’s simple to pilot on a subset of users while keeping passwords as fallback.

On the performance side, automatic memory‑pool eviction addresses a common long‑running service issue: buffers that linger and inflate process memory. ASP.NET now returns idle memory to the OS more predictably, which cuts tail‑latency incidents when the GC competes with other workloads. Minimal APIs pick up better typed results, including a straightforward server‑sent events helper to stream progress without dragging in a full realtime layer.

Observability also improves. New metrics across Identity, authn/authz, Blazor, and the memory pool make it easier to alert on what matters, not just CPU graphs. If you struggled to answer “why did sign‑in get slow last Tuesday?” you’ll appreciate the added signals.

C# 14: fixes for code you write every day

C# 14 focuses on ergonomics that reduce ceremony without magic. Field‑backed properties let you keep custom getters/setters while referencing the implicit field—great for trimming noise instead of yo‑yo‑ing between auto‑properties and hand‑rolled backing fields. Extension members move beyond methods to properties and static members, making it easier to “teach” types you don’t own without wrapper classes.

Other small wins add up: null‑conditional assignment (?.=) cuts boilerplate for lazy init; modifiers on simple lambda parameters (ref, in, out) avoid awkward rewrites; more implicit conversions for Span<T> reduce friction in hot paths; user‑defined compound assignment operators let advanced authors eliminate copies. None of these features force rewrites, but they clean up code reviews and simplify performance‑minded APIs.

Runtime and libraries you’ll actually feel

The runtime team has been chipping away at abstraction overhead for years, and .NET 10 keeps that tempo. The JIT’s improved devirtualization and smarter inlining show up in everyday patterns—like array enumeration—without code changes. A revamped code‑layout strategy packs hot paths more tightly, improving branch prediction and instruction cache density.

NativeAOT takes another step forward with smaller, faster binaries, which matters for utility services, CLIs, and serverless handlers. On the libraries side, networking gets a cleaner WebSocketStream API and TLS 1.3 on macOS; JSON serialization tightens safety (e.g., duplicate property handling) while pushing throughput; and cryptography expands post‑quantum options (ML‑DSA/ML‑KEM variants) for organizations starting PQC evaluations.

Security backdrop: why patching Kestrel and moving to LTS go together

In October, Microsoft shipped patches for a high‑severity request‑smuggling issue in Kestrel affecting ASP.NET Core 8/9 and prereleases of 10. The safe path is to be on the patched baselines (8.0.21, 9.0.10, or 10 RC2+ and then GA). If your estate mixes versions, centralize on .NET 10 LTS so you’re not juggling divergent servicing schedules. While you’re there, adopt the safer JSON defaults and add endpoint‑level SSE throttling to keep long‑lived connections from masking abusive traffic.

The .NET 10 LTS upgrade playbook

Here’s a lean, battle‑tested plan that works for most product teams. Treat this as a repeatable pattern across services.

1) Inventory and segment

Make an accurate list of apps, TFMs, hosting models, and dependency hotspots. Tag each service with: traffic tier (S/M/L), change risk (low/medium/high), and CI/CD coverage quality. High‑traffic but low‑risk services go first to buy confidence and monitoring improvements early.

2) Prep your toolchain

Install the .NET 10 SDK across build agents and dev machines. If you target net10.0, roll Visual Studio 2026 to all contributors on that repo. Pin SDKs via global.json so local builds and CI match.

3) Lift the TFM safely

In each project file, update <TargetFramework>net10.0</TargetFramework> (or add to TargetFrameworks for libraries). For ASP.NET Core projects, run a clean restore and scrutinize transitive packages that pin older frameworks. Keep your first PR minimal: TFM bump, package updates, and any build‑break fixes. No “while we’re here” refactors.

4) Update platform dependencies

Bring ASP.NET Core, EF Core, and major libraries to their .NET 10‑compatible lines. Verify your reverse proxy (Nginx/Apache/YARP) and HTTP pipeline settings, especially if you rely on request buffering, size limits, or WebSocket/SSE upgrades. For EF Core, check provider versions (SQL Server, PostgreSQL, Cosmos DB) and turn on new tracing hooks in staging first.

5) Turn on diagnostics before traffic

Enable the new built‑in metrics for Identity, auth, and Blazor if applicable. In API‑only services, add Kestrel and memory‑pool metrics to dashboards. If you publish containers, take advantage of SDK improvements: console apps can now build images with a single publish target, and you can explicitly set image format. Bake these into your pipeline templates once, then stamp out across repos.

6) Exercise C# 14 where it counts

Don’t rewrite; opportunistically apply C# 14 in hot paths and libraries. Good targets: code that manipulates spans and buffers, property‑heavy models (field‑backed properties), and utility extensions that keep leaking into helper classes. Add analyzers and a short style note so PRs converge naturally.

7) Security pass

Confirm your Kestrel baseline is patched, switch to stricter JSON options where viable, and pilot passkeys for a low‑risk audience like employees or beta testers. Document rollback criteria. Make sure secrets stay out of code and move to your standard vault if you’re not already there—.NET 10 plays nicely with that pattern.

8) Roll out with real guardrails

Use canary and traffic splitting, not toggles alone. Gate promotions on latency p95/p99, 5xx rate, and memory growth under steady load. If you serve SSE, validate connection lifetimes and backpressure. Only after a full business cycle without surprises should you cut the old TFM from the repo.

Hands‑on: a minimal service upgrade

Let’s get practical. Suppose you have a minimal API on net8.0. This is the skeleton of a safe net10.0 move.

1) Update the project file:

<TargetFramework>net10.0</TargetFramework>

2) Restore and update ASP.NET Core packages to the 10.0 wave (or rely on the shared framework).

3) Add server‑sent events to stream long jobs without polling:

app.MapGet("/jobs/{id}/events", (string id) => TypedResults.ServerSentEvents(async writer => { /* write events */ }));

4) Turn on passkeys (pilot in dev/staging first) using the new Identity helpers and Blazor template if you host UI.

5) Publish your container with the SDK target, and set the image format explicitly if your registry enforces it.

People also ask

Is .NET 10 LTS stable enough for production?

Yes. It’s the supported LTS line with three years of fixes. If you’re on .NET 8 LTS or 9 STS, the migration cost is modest and you gain performance, safer defaults, and a consolidated servicing story.

Do I need Visual Studio 2026 to target net10.0?

To compile projects that target net10.0, yes—use VS 2026 (18.x) or newer. You can still build older TFMs with the .NET 10 SDK on VS 17.14, but you won’t target .NET 10 directly.

Will my .NET 8/9 apps run unmodified on .NET 10?

Most do after a retarget and package updates. Expect minor breaks around analyzers, tighter JSON options, or obsolete APIs. Keep your first PR small, let CI catch regressions, and use multi‑TFM libraries if you must support older hosts during rollout.

How does C# 14 affect existing code?

Nothing breaks. You opt into features as you touch code. The wins come from smaller diffs and less ceremony—especially in models, extension‑heavy libraries, and performance‑sensitive paths.

A quick risk checklist before you flip traffic

• IDE/tooling: all contributors upgraded; global.json pins the SDK.
• Runtime baselines: patched builds across Kestrel and ASP.NET Core; CVE backlog is empty.
• Observability: new ASP.NET metrics wired; memory‑pool and auth graphs visible.
• Dependencies: EF Core provider versions verified; minimal APIs and OpenAPI packages aligned.
• Deployment: container image format set; SBOM published; rollbacks tested.

What to do next

For dev leads: schedule a two‑sprint migration wedge and ship 1–3 services on .NET 10 LTS using the playbook above. Add the diagnostics first, then the TFM bump, then performance opportunities. For product and business owners: fund the IDE/runtime rollout and a security bake‑off with passkeys. Aim for measurable p95 latency and cost‑per‑request wins, not just “we upgraded.”

If you want a deeper, structured path, our team has written a complete .NET 10 LTS upgrade guide and a battle‑tested 7‑day plan you can run with your platform group. If your CI/CD relies on GitHub Actions, double‑check your security posture around pull requests—here’s our take on the pull_request_target changes and safer defaults. And if you’d rather not go it alone, explore our services or reach out via contacts—we’ve been migrating teams since the .NET Core 1.0 days.

Zooming out

The best time to modernize is when you can trade a small, predictable amount of work for several years of stability and measurable performance gains. That’s the exchange on the table with .NET 10 LTS. Ship it deliberately: tighten your diagnostics, patch what’s known, adopt a couple of C# 14 wins, and move the portfolio. Your future incidents—and your weekend—will thank you.