.NET 10 LTS: What’s New and the 30‑Day Upgrade Plan

.NET 10 LTS officially landed on November 11, 2025, with mainstream support through November 14, 2028. That makes it the long-term anchor for teams deciding where to place their next three-year bet. If you’re still on .NET 8 LTS or running .NET 9 STS, the support runway and security posture both favor a move now—not next quarter. (dotnet.microsoft.com)

Here’s the thing: this release isn’t just a “.0 bump.” C# 14 brings real ergonomics, ASP.NET Core 10 modernizes APIs and auth, EF Core 10 taps vector search and native JSON on Azure SQL/SQL Server 2025, and the runtime shaves latency in the places you actually feel it. Below, I’ll hit the features that matter, the dates you can’t ignore, what might bite during the jump, and a step-by-step 30‑day upgrade plan you can run with your team.

What’s in .NET 10 LTS that actually moves the needle

C# 14: less boilerplate, more expressiveness

The companion C# 14 release packs several quality-of-life upgrades: extension members (including properties and static members), field-backed properties (no more manual private backing fields), null‑conditional assignment (using ?. on the left side of =), implicit span conversions, modifiers on simple lambda parameters, and more. These are small on paper, big in day-to-day code. (learn.microsoft.com)

Two callouts for teams: extension members will change how your platform libraries expose helpers—use them to consolidate cross‑cutting functionality without polluting types you don’t own. And field‑backed properties make defensive property logic easier to express without losing clarity. If you’re standardizing across repos, document where you want extension blocks and when field‑backed properties are preferred to keep code reviews sane. (learn.microsoft.com)

ASP.NET Core 10: security, specs, and diagnostics that matter

ASP.NET Core in .NET 10 adds built-in passkey support (WebAuthn/FIDO2) in Identity, enabling phishing-resistant, passwordless auth flows—with templates wired in for Blazor Web App. It also brings automatic memory pool eviction to reduce long‑running process bloat, plus a diagnostics pass that lights up Identity metrics for better production visibility. (devblogs.microsoft.com)

On the API side, OpenAPI 3.1 is now first-class in the framework, aligning with JSON Schema 2020-12 and unblocking modern tooling. That lands alongside major updates to the OpenAPI.NET library and Swashbuckle’s .NET 10 support (note: Swashbuckle v10 has breaking changes and 3.1 is opt-in). If your docs pipeline still targets 3.0, plan the switch—your clients and generators will thank you. (learn.microsoft.com)

Passkeys aren’t a silver bullet—you still own enrollment UX, device fallback, and policy. But they’re a practical step up from passwords for consumer and enterprise apps alike, and they’re officially in the box now. (devblogs.microsoft.com)

EF Core 10: ready for vector search and native JSON

EF Core 10 embraces two big database capabilities that ship with Azure SQL and SQL Server 2025: a native vector data type with a VECTOR_DISTANCE() function for semantic search, and a native JSON data type with JSON aggregates. EF 10 understands both, and it can default to the JSON type when you target Azure SQL or SQL Server 2025 (compat level 170+). That means simpler models, better performance, and fewer hand-rolled shims. (learn.microsoft.com)

If you’ve been deferring “AI-ish” search because of infrastructure drag, the built‑in vector stack removes excuses—your relational store can now handle the embeddings pipeline end‑to‑end, and EF Core gives you clean patterns to query it. For JSON-heavy domains, moving from NVARCHAR to the native JSON type eliminates a class of stringy foot‑guns and improves query performance; JSON indexing is also in preview for SQL Server 2025. (techcommunity.microsoft.com)

Runtime performance: faster by default, with fewer abstractions showing through

.NET 10’s runtime continues the “de‑abstraction” effort: smarter JIT inlining, better devirtualization, improved array enumeration, new code layout heuristics, and expanded vectorization. In real workloads, those show up as lower CPU and shorter tail latency—often with zero code changes. A Microsoft deep-dive details the specific JIT improvements and where the wins come from. (learn.microsoft.com)

Independent teams are also reporting concrete gains—for example, a JSON Schema validation library saw ~18% improvement moving to the .NET 10 runtime (and ~29% if you’re going from .NET 8 LTS straight to 10). Your mileage will vary, so budget time for profiling; but the “free speed” is real. (endjin.com)

Is .NET 10 LTS worth the hop from .NET 8?

Short answer: yes, for most teams. .NET 10 is LTS and supported until November 14, 2028. .NET 8 LTS and .NET 9 STS both exit support on November 10, 2026. If you adopt 10 in Q4 2025 or early 2026, you avoid a scramble in late 2026 and can plan one major framework move before 2028. (dotnet.microsoft.com)

There’s also a security nudge. In October 2025, Microsoft published a critical HTTP request smuggling vulnerability (CVE‑2025‑55315) affecting Kestrel across 2.x, 8, 9, and early .NET 10 RC builds. Patches shipped promptly, but it’s a timely reminder: the faster you move to the actively serviced LTS, the lower your operational risk. Validate that your runners, containers, and hosting bundles pulled the patched builds. (github.com)

What breaks when you flip to C# 14?

Most apps compile cleanly, but a few areas need attention:

• Extension members: Codify where extension blocks live (e.g., a “*.Extensions” project) and how you test them. Without conventions, discoverability becomes a tax.
• Field‑backed properties: Great for concise guards; just be explicit about exception types and messages in shared libraries so behavior changes don’t surprise downstream teams.
• Implicit span conversions: This is a gift for performance code, but watch for accidental allocations or lifetime issues hidden by the new conveniences in complex async paths.

If you need a gate, set LangVersion per project and phase features into your guidelines; you can adopt the SDK and runtime now while keeping language usage conservative until your linters and reviews catch up. (learn.microsoft.com)

.NET 10 LTS upgrade plan you can execute in 30 days

This is the playbook we’ve used on mid‑sized product suites (10–40 services, 3–6 web UIs, shared packages). Adjust the cadence to your risk profile and deploy windows.

Week 1 — Inventory, pins, and safety rails

Make an explicit inventory: solutions, TFMs, NuGet packages, hosting bundles, container bases, self‑contained vs. framework‑dependent deployments, and CI runners. Add temporary safety rails:

• Pin toolchains: In each repo, commit a global.json pointing to your chosen .NET 10 SDK. In containers, pin base images by digest, not tag.
• Freeze broken dep updates: Enable a blocklist for packages known to lag .NET 10 support (e.g., pre‑v10 Swashbuckle if you rely on OpenAPI generation). Plan their upgrades deliberately. (newreleases.io)
• Baseline perf: Capture p95/p99 latency and CPU for 2–3 representative flows per service. You’ll need these numbers in Week 4.

Week 2 — Lift the platform, keep language usage stable

Adopt the .NET 10 SDK and TFM (net10.0) across a pilot slice first. Keep LangVersion at the team’s current standard to isolate runtime/framework effects. Update ASP.NET Core and EF packages together; for API projects, decide now if you’ll move your OpenAPI toolchain to 3.1 this cycle or defer one sprint. (learn.microsoft.com)

For data-heavy apps that plan to adopt SQL Server 2025 features later, add compatibility tests and a migration sketch for moving JSON columns to the native type. You’re laying track for a future migration—no need to switch the storage type in this 30‑day window. (techcommunity.microsoft.com)

Week 3 — Feature toggles and auth

Introduce C# 14 features surgically where they replace repetitive patterns (e.g., field‑backed properties in DTO validators, extension blocks for common collection helpers). For authentication, prototype passkeys behind a feature flag in one user journey. Validate registration, recovery, and telemetry before you roll it wider. (devblogs.microsoft.com)

On API projects, if you do move to OpenAPI 3.1 now, run the new document through your client generators and docs UI. Swashbuckle v10 changes are breaking; schedule time for its migration guide and keep 3.1 opt-in until your ecosystem is green. (newreleases.io)

Week 4 — Perf, security, and rollout

Re‑run your Week 1 perf scenarios, compare to baselines, and hunt regressions. The .NET 10 runtime usually wins, but hotspots happen—sometimes due to environment differences, not the framework. Patch the Kestrel CVE if your images or hosting bundles predate mid‑October 2025, double‑check Identity metrics are flowing, and green‑light production after one live‑traffic canary. (github.com)

People also ask

Should we skip .NET 9 STS and move straight to .NET 10 LTS?

Yes. .NET 9 STS and .NET 8 LTS both end support on November 10, 2026. Jumping to 10 now buys you three years of coverage, time for one more major move before 2028, and avoids a late‑2026 crunch. (dotnet.microsoft.com)

Do we need to upgrade Visual Studio to adopt C# 14?

Use the latest Visual Studio 2022 with the .NET 10 SDK (and of course CLI builds are fine). The C# 14 feature set is documented for .NET 10 and supported with current VS releases. (learn.microsoft.com)

What about OpenAPI 3.1—will it break our docs?

It might, depending on your tooling. ASP.NET Core can generate 3.1 documents, OpenAPI.NET shipped major updates, and Swashbuckle v10 supports .NET 10 with opt‑in 3.1. Test your pipeline; keep 3.0 if needed and schedule the 3.1 move as a tracked task. (learn.microsoft.com)

Risks and edge cases (be candid)

- Tooling drift: If your CI images lag, a “works on my machine” sweep is inevitable. Pin SDKs and runner images explicitly.
- OpenAPI stack churn: Multiple moving pieces (framework, OpenAPI.NET, Swashbuckle) mean you should treat spec updates as a mini‑project, not a checkbox.
- Perf regressions: Rare, but real. That’s why Week 1 baselines and Week 4 comparisons exist. Keep profiling in the loop; don’t rely on averages alone. (devblogs.microsoft.com)

What to do next

• Decide today whether OpenAPI 3.1 and passkeys are part of this upgrade or a follow‑up sprint. Write it down, avoid scope creep. (learn.microsoft.com)
• Pick one flagship service and one internal app as pilots. Run the 30‑day plan, then templatize the changes for the rest of your estate.
• If your stack spans ecosystems, align your platform cadence—our Node.js 24 LTS upgrade playbook shows how we manage multi‑language LTS cycles without thrash.
• Want a second set of eyes? Our what we do page outlines the upgrade accelerators we run for clients, and our .NET 10 LTS upgrade reality check dives deeper into sequencing, testing, and rollback planning. Or just get in touch.

Zooming out

.NET 10 LTS is the most convincing “just do it” release since .NET 6: long support window, fewer migration headaches than many feared, and features that map to real‑world backlogs—security hardening, modern API specs, faster code, and a cleaner data layer. Treat the move as a short, disciplined project, not a background chore. Ship one pilot, codify the patterns, and roll forward. Your future self—staring down the 2026 support wall—will be very happy you did.