.NET 10 LTS landed on November 11, 2025 with a three‑year support window through November 14, 2028. If you own customer‑facing APIs or SaaS on .NET 6–9, this is the most sensible point to standardize, patch, and reclaim performance headroom before year‑end code freezes. The goal of this guide: explain what changed, why it matters for uptime and cost, and give you a 30‑day rollout you can run without heroics. (dotnet.microsoft.com)
What’s actually new (and useful) in .NET 10
The headline is that .NET 10 is an LTS release, but the substance is in the runtime, libraries, and ASP.NET Core improvements. On the runtime side, you get better JIT inlining and devirtualization, improved stack allocations, AVX10.2 support for modern CPUs, and more mature NativeAOT—together these translate to lower p95 latency and smaller memory footprints in real workloads. (learn.microsoft.com)
In the base libraries, Microsoft added practical APIs: WebSocketStream so you can treat WebSockets like a Stream; strict JSON modes to reject duplicate properties; and expanded post‑quantum cryptography (ML‑DSA/SLH‑DSA/ML‑KEM variants) for systems that need future‑safe key exchange and signatures. If you’re in regulated industries or planning long‑lived data protection, that last one is not academic. (learn.microsoft.com)
ASP.NET Core 10: security, observability, and fewer footguns
ASP.NET Core 10 doubles down on production concerns. Identity adds passkey (WebAuthn/FIDO2) support out of the box—goodbye SMS OTP drift. There’s automatic memory‑pool eviction to hand unused buffers back to the OS in long‑running services, Server‑Sent Events helpers for real‑time streams, and a cleaner way to produce consistent ProblemDetails responses. You also get richer built‑in metrics across Identity, auth, and Blazor. These aren’t gimmicks: they cut toil in day‑two operations. (devblogs.microsoft.com)
On client‑side and interactive apps, Blazor gained better diagnostics and state handling, making hybrid render modes less fragile. If you’ve been hesitant to lean on Blazor for authenticated dashboards, the stability and metrics story is improving. (devblogs.microsoft.com)
C# 14: upgrades you’ll actually use
C# 14 focuses on ergonomics without sacrificing clarity. You’ll notice field‑backed properties (use field in accessors instead of adding a separate backing field), extension members (including properties and static members in extension blocks), null‑conditional assignment (customer?.Order = ...), more span‑friendly conversions, and modifiers on simple lambda parameters. These cut boilerplate and help performance‑sensitive code read like intent rather than plumbing. (learn.microsoft.com)
EF Core 10: pragmatic features plus vectors
EF Core 10 ships with targeted improvements, but one stands out for search and AI‑adjacent scenarios: first‑class support for the vector data type and the VECTOR_DISTANCE() function in Azure SQL and SQL Server 2025. If your app mixes relational data with embeddings—for semantic search, RAG, or recommendations—this lets you keep more of the stack inside your primary database with fewer sidecars. (learn.microsoft.com)
Security first: the Kestrel request‑smuggling fix you can’t ignore
In October, Microsoft patched a Kestrel HTTP request‑smuggling issue (CVE‑2025‑55315) with a CVSS score of 9.9—described as “our highest ever.” Practically speaking, exploitability depends on your proxy topology and app code, but the worst‑case outcomes include credential exposure, CSRF bypass, and file tampering. If you run ASP.NET Core 8/9 or older Kestrel packages, you needed the October patches; if you’re moving to .NET 10 now, you get the fix as part of the upgrade path. (theregister.com)
The advisory lists patched versions (for example, Kestrel 2.3.6 for 2.x apps and ASP.NET Core updates for 8.0.21/9.0.9/10 RC2+). Don’t roll this into “later”—close the window before you begin any migration. At minimum, update your build image or hosting bundle, restart services, and verify logs at the proxy layer for anomalies. (github.com)
Where .NET 10 runs on day one (good news for Linux)
As of November 17, Red Hat published .NET 10 for RHEL 10.1/9.7/8.10 and OpenShift, with updated container images. If your platform standardizes on UBI runtimes or OpenShift, you can pilot on vendor‑supported bits immediately. This matters for enterprises that require distro‑supplied packages and signed containers before any production rollout. (developers.redhat.com)
The .NET 10 LTS upgrade playbook
Here’s the path we’ve used with product teams that need results fast and safe. It assumes you’re on .NET 8 or 9. If you’re older, add a pre‑step to land on 8 first and delete incompatible frameworks.
1) Patch current prod before touching code
Apply October’s ASP.NET Core/Kestrel updates on your current stack. Validate at the edge (e.g., Envoy/Nginx/Azure Front Door) that smuggled requests are blocked. This reduces your exposure while you prepare the .NET 10 LTS cutover. (theregister.com)
2) Inventory and risk‑rank
List every service, runtime, and library with versions. Flag apps with: direct Kestrel exposure, custom middleware that rewrites requests, reflection‑heavy code, or unsafe span usage. These are your canary candidates and your potential footguns with C# 14 and new trimming/AOT behaviors.
3) Build once, run everywhere
Upgrade CI images to the .NET 10 SDK and pin reproducible container bases. If you’re on RHEL/UBI or OpenShift, switch to the .NET 10 images so ops isn’t juggling mismatched layers. The build stage should surface language warnings from C# 14 and shipping analyzers. (developers.redhat.com)
4) Target framework bump, no functional changes
Change Tfm to net10.0, upgrade ASP.NET Core packages, and keep behavior stable. Turn on strict JSON duplicate‑property rejection in staging to flush bad clients early. Enable the new Identity and HTTP metrics so you can compare apples to apples once traffic flows. (learn.microsoft.com)
5) Adopt the “low‑risk, high‑ROI” bits first
Use field‑backed properties and extension members to simplify hot paths where it’s obvious and covered by tests. Don’t start a refactor crusade—focus on the two or three code areas that affect latency or maintainability the most. (learn.microsoft.com)
6) Observability contract
Add the new ASP.NET Core meters to your dashboards, especially Identity and memory‑pool metrics. Set service‑level golden signals with p50/p95/p99 latency, GC pause totals, and a budget for socket/HTTP allocation spikes. These numbers will tell you when NativeAOT or trimming is worth the effort versus regular JIT. (devblogs.microsoft.com)
7) Where NativeAOT fits
For small, spiky utilities (webhooks, queue workers), NativeAOT can shave cold start and RAM. For larger monoliths or plugin‑heavy apps, treat AOT as a follow‑on experiment—test startup time, size, and reflection coverage in a branch. The AOT story keeps improving, but you shouldn’t bet your core product on it until perf graphs and error budgets say so. (learn.microsoft.com)
8) EF Core 10 vectors if you need them
If you currently ship embeddings to a separate vector store but your RPO/RTO posture favors fewer moving parts, pilot EF Core 10’s vector type against Azure SQL/SQL Server 2025. Use it for re‑ranking or feature toggles before you move any primary search paths. (learn.microsoft.com)
9) Canary and cutover
Push a canary that receives 5–10% of production traffic with detailed logging. Compare error rates, latency, and memory against baseline for 48–72 hours. If stable, roll to 50%, then 100% during a low‑risk window. Keep the old environment warm for a full business cycle (billing, batched jobs) before you dismantle it.
How long will this take?
For healthy codebases on .NET 8/9, teams we coach typically ship the first production workload on .NET 10 LTS in 1–2 weeks. Full fleet standardization spans 30–45 days, mostly because of dependencies and test depth. If you want a deeper calendarized version, our .NET 10 LTS 30‑Day Upgrade Plan lays out a day‑by‑day sequence you can copy.
Performance expectations you can defend
Because .NET 10 folds in JIT and library work plus ASP.NET Core’s memory‑pool eviction, you’ll usually see lower steady‑state memory and tighter tail latency. Your mileage depends on GC settings, allocator behavior in your container runtime, and how much dynamic code your app relies on. Treat it like any serious change: collect baselines, run load, and analyze flame graphs until you can articulate where the wins came from. (learn.microsoft.com)
People also ask
Is C# 14 required to use .NET 10 LTS?
No—projects can target net10.0 while staying on your existing language version. That said, C# 14 ships with the SDK and is stable; adopting features like field‑backed properties and extension members is a low‑risk way to cut noise in hot code paths. (learn.microsoft.com)
Do we need to jump to EF Core 10 immediately?
Only if you want its features (e.g., vector support) or you need to stay aligned with .NET 10 for support. EF Core follows .NET’s cadence; mixing EF versions works within constraints, but aligning reduces surprises when you later adopt trimming or AOT. (learn.microsoft.com)
Will ASP.NET Core passkeys require new hardware for users?
Not necessarily. WebAuthn works with platform authenticators built into iOS, Android, and modern desktops. Many users can register passkeys using their phone or laptop biometrics; FIDO2 security keys are optional for higher assurance. ASP.NET Core Identity now includes passkey support in its templates, making it straightforward to light up. (devblogs.microsoft.com)
When does .NET 9 support end, and why standardize now?
.NET 9 is STS and supported until November 10, 2026. If you’re on 9, you have breathing room—but consolidating on .NET 10 LTS today saves you from a rushed migration in 2026 and lets you pocket performance and security improvements this quarter. (dotnet.microsoft.com)
Common pitfalls we’ve seen (and how to avoid them)
Silent JSON behavior changes. Turning on duplicate‑property rejection will flush out client issues. Stage it first; don’t surprise mobile apps on Friday. (learn.microsoft.com)
Over‑ambitious refactors. C# 14 is enticing. Use it surgically in covered areas. Save sweeping changes for after you’ve stabilized on .NET 10 LTS. (learn.microsoft.com)
Ignoring distro support. If your infosec requires vendor‑signed runtimes, wait for your target Linux vendor’s images. Red Hat and others are already shipping .NET 10; align your base images before canaries. (developers.redhat.com)
NativeAOT everywhere. It’s a fantastic tool—but its sweet spot is small, focused apps. Validate feature parity and reflection needs before committing. (learn.microsoft.com)
What to do next
• Patch current production for CVE‑2025‑55315 and verify at your proxy tier.
• Upgrade CI images to the .NET 10 SDK and switch container bases to supported vendor images.
• Bump TFM to net10.0, keep behavior stable, enable metrics, and run load tests.
• Adopt C# 14 in hot paths, not across the repo.
• Pilot EF Core 10 vectors only if you have an embeddings use case.
• Canary 10% traffic for 48–72 hours, then roll forward.
If you want a second set of eyes on your plan, our team ships these upgrades with real SLOs and KPIs. Start with our frank take in The .NET 10 LTS Upgrade Reality Check, browse how we approach rollouts on the services page, and see examples on our portfolio. Then send us your repo map and target dates—we’ll turn it into a concrete, testable cutover plan.
Zooming out
.NET 10 LTS isn’t about shiny tech for slide decks. It’s a timely consolidation: performance work that drops infrastructure cost, safer defaults that reduce pager duty, language changes that make code easier to reason about, and a patched web stack you can defend to a security review. Shipping it is straightforward if you treat it like any other operational change—measure, stage, canary, and learn. The teams that do that now will be heads‑down on product in Q1, while everyone else is wrestling with rushed migrations later.
