.NET 10 LTS is here, released on November 11, 2025 with three years of support through November 10, 2028. If your roadmap touches anything in ASP.NET Core, EF Core, or C# 14, this is the train to board. The shift isn’t just marketing—runtime performance improvements, stronger identity primitives, and practical SDK upgrades add up to a safer, faster platform for the next cycle of your product. (devblogs.microsoft.com)

Team planning a .NET 10 LTS upgrade on a whiteboard

What’s actually new in .NET 10 LTS?

Here’s the thing: most teams don’t adopt a major version for vanity. You move because it reduces risk, unlocks capability, or makes the same hardware do more work. .NET 10 brings improvements across the runtime (JIT inlining, devirtualization, stack allocations), hardware acceleration (AVX10.2 on modern Intel, Arm64 SVE), and Native AOT quality-of-life upgrades that shrink binaries and startup. That cascades into real capacity gains when you’re serving spiky traffic. (learn.microsoft.com)

On the web stack, ASP.NET Core 10 adds automatic memory pool eviction (less long‑tail memory bloat in busy services) and passkey support (WebAuthn/FIDO2) in Identity. Minimal APIs gain niceties, OpenAPI tooling is better, and you get new metrics and diagnostics baked in—handy when SREs are chasing a perf regression. Blazor picks up preload and tracing improvements that help with first‑paint and live diagnostics. (devblogs.microsoft.com)

In the SDK, you’ll notice smoother CLI ergonomics, one‑shot tool execution, container image support for console apps, and improved tool compatibility via the any RuntimeIdentifier. Those small wins add up when you script CI pipelines. (learn.microsoft.com)

.NET 10 LTS: the features that move the needle

Performance is the headline, but it’s the elimination of toil that sticks. NativeAOT maturity means smaller, faster single‑file apps for microservices and CLIs. The runtime’s SIMD and codegen work means fewer hotspots in CPU profiles. The team even called out Arm64 GC write‑barrier improvements that cut certain pause times by roughly 8–20%, which you’ll feel under load on newer hardware. (devblogs.microsoft.com)

Security gets a lift too. Beyond Identity’s passkey support, the libraries expand cryptography and networking APIs, including stricter JSON serialization options and TLS 1.3 improvements on macOS clients. These aren’t flashy, but they close real gaps in enterprise orgs where every audit asks the same questions. (learn.microsoft.com)

Is C# 14 worth adopting on day one?

Short answer: yes—selectively. C# 14 ships field‑backed properties, extension members, and more ergonomic span conversions. Field‑backed properties give you a clean, incremental path from auto‑props to hand‑rolled accessors, so you can inject validation or tracing later without rewriting call sites. Extension members reduce friction when you want domain‑fluent APIs without polluting core types. And the Span/ReadOnlySpan improvements smooth performance‑sensitive code without contortions. (learn.microsoft.com)

Adoption strategy: enable the language in new services first, then backfill hotspots in existing code. Lint aggressively; treat new features as “opt‑in for maintainers,” not “firehose for the whole team.” That keeps your codebase coherent while you collect real‑world feedback.

EF Core 10: what changes for data‑heavy apps?

EF Core 10 aligns with .NET 10 and brings concrete upgrades, notably vector search and a first‑class JSON type for Azure SQL/SQL Server 2025. If you’re experimenting with embeddings—recommendations, semantic search—vector support eliminates awkward shims. The JSON type finally moves beyond nvarchar blobs with safer, more efficient storage and modifiers. Important: EF maps the JSON type automatically when your compatibility level is 170+; older SQL Server versions still work, but won’t get the native JSON benefits. (learn.microsoft.com)

Operationally, EF’s named query filters are a quiet but powerful addition. You can keep soft‑delete and multitenant filters separate, then disable only what a particular query needs. It prevents those “one giant global filter” hacks that make diagnostics miserable later. (learn.microsoft.com)

Performance dashboard showing improved latency after .NET 10 upgrade

There’s a security reason to move now

In October, Microsoft patched a critical HTTP request smuggling flaw in Kestrel (CVE‑2025‑55315) rated 9.9 CVSS—framed internally as their “highest ever” for ASP.NET Core. The impact depends on your topology and code paths, but downstream proxies and inconsistent parsing can enable security feature bypasses. Patches landed across supported trains, and RC2 builds incorporated the fix going into .NET 10 GA. If your estate includes older self‑contained deployments, you must rebuild and redeploy to pick up the runtime fixes. (theregister.com)

If that sounds abstract, consider how vendors reacted: QNAP issued an alert urging immediate updates for Windows endpoints because their agent depended on ASP.NET Core bits. That’s the real‑world blast radius—SDK/runtime vulnerabilities often surface in “unrelated” software. The lesson: centralize your runtime versioning, inventory self‑contained apps, and retire stragglers before they become breach root‑cause reports. (techradar.com)

Primary keyword check: .NET 10 LTS upgrade strategy

Let’s get practical. Your .NET 10 LTS upgrade strategy should start with an explicit goal: either unlock capacity (reduce compute per request), shrink operational risk (patch posture, Identity hardening), or ship new customer value (C#/EF features you can’t backport). Map the goal to a 30‑day sprint and treat everything else as backlog. That’s how you avoid “rolling upgrade” purgatory.

The 3×3 upgrade framework we use with teams

Phase 1 — Discovery (days 1–7)

1) Inventory: enumerate apps, their hosting model (Framework‑dependent vs self‑contained), and exposed endpoints. 2) Dependencies: capture SDK/runtime versions, ASP.NET Core, EF Core, and key NuGet packages. 3) Risk flags: admin endpoints, custom auth handlers, reverse proxies, and any home‑rolled middleware touching headers. This guides where you run canary builds first. Tie the inventory to CI so it stays current.

Phase 2 — Build & verify (days 8–18)

4) Create a .NET 10 branch, bump target frameworks, and switch CI to multi‑TFM for critical packages. 5) Turn on C# 14 for only the projects you’ll touch; set analyzers to warning‑as‑error for unsafe conversions. 6) Replace deprecated APIs and re‑generate OpenAPI; validate with contract tests. 7) Measure: run load tests for a golden path and a heavy query path; capture CPU, latency distribution (p95/p99), and memory churn. 8) Security drills: add a request‑smuggling test harness in front of Kestrel to validate proxies; verify passkey auth flows in staging with real devices.

Phase 3 — Rollout (days 19–30)

9) Ship a canary to 5–10% of traffic with auto‑rollback. 10) Watch memory pool eviction over a full diurnal cycle; compare to baseline. 11) Promote to 50% when error budgets hold, then to 100% with a dark‑launch feature flag for Identity changes. 12) Schedule a post‑launch pit stop to clean up analyzer suppressions and remove dead code.

Benchmarks and numbers that matter

Numbers are context‑heavy, but some are broadly useful. The runtime adds AVX10.2 support and better struct argument codegen; together with improved inlining and devirtualization, hot paths often tighten without source changes. On Arm64, GC write‑barrier work can shave roughly 8–20% off certain pause patterns. And NativeAOT progress continues to trim startup and memory—especially for small services where cold starts cost user patience. Validate these in your environment, but expect a meaningful “free lunch” on modern hardware. (learn.microsoft.com)

Hidden gotchas and migration traps

Self‑contained deployments: patching the host OS won’t update your bundled runtime. After Kestrel’s CVE, teams discovered dozens of forgotten services still pinning old runtimes. Make “rebuild and redeploy” a compliance item and alert on outdated self‑contained bundles in artifact storage. (herodevs.com)

Proxy assumptions: if you rely on a reverse proxy to normalize traffic, make sure its request‑smuggling mitigation aligns with Kestrel’s parser—especially around Content‑Length and Transfer‑Encoding edge cases. Run an active test during rollout; don’t assume defaults are safe. (theregister.com)

Identity changes: passkeys lower friction, but they change your support scripts. Plan for account recovery UX, shared device policies, and admin override flows. Add telemetry so your team can see passkey adoption rates and failure causes.

EF Core 10 JSON and vectors: adopting the native JSON type can change storage footprints and indexing behavior. Migrate a subset first, create targeted indexes, and verify that query plans don’t regress under multi‑tenant load. (learn.microsoft.com)

Cost framing for decision‑makers

The ROI here is straightforward. If .NET 10 reduces CPU per request by even mid‑single digits across your busiest APIs, your cloud bill and headroom improve immediately. Add security posture (patch currency, fewer bespoke auth flows) and maintenance velocity (C# 14, SDK ergonomics), and the upgrade pays back within a quarter for most SaaS back ends. The key is to time‑box the work and measure before/after to prove it.

What to do next (developers)

• Install the .NET 10 SDK and update your local toolchains. • Create a branch that bumps target frameworks and C# language version for one service. • Regenerate OpenAPI and run contract tests. • Add load tests that record p95/p99 latency, GC pauses, and memory high‑water marks. • Validate passkeys in staging with real devices and recovery flows. • Rebuild any self‑contained apps and redeploy to capture security fixes. (learn.microsoft.com)

What to do next (engineering leaders)

• Pick one user‑facing API and one internal service as your .NET 10 pilots. • Make success criteria explicit: latency, error budget, and compute per request. • Book a 30‑day modernization sprint and gate it in your roadmap. • Stand up a weekly risk review for CVEs and dependency drift. • Socialize a conservative C# 14 adoption guideline to keep the codebase coherent.

Where we can help

If you’d rather not put your roadmap at risk, our team has shipped multiple .NET 10 upgrades with hard deadlines. Start with our field notes in Ship .NET 10 LTS: What’s New and How to Upgrade, then grab our 7‑day upgrade plan if you need velocity. Want hands‑on help? Explore our modernization sprints and platform services, or book a working session to scope your pilot. We’ll meet you where your stack is—no rewrites, just focused changes that move metrics.

Zooming out

.NET 10 LTS isn’t a flashy rewrite; it’s a well‑judged release that hardens your web tier, unlocks useful language features, and trims waste—especially at scale. With concrete security fixes fresh in mind, the safest posture for most organizations is to plan a .NET 10 migration now, not “sometime next year.” Give a small cross‑functional team a 30‑day runway, measure everything, and hold the line on scope. You’ll end the month with fewer pagers, more headroom, and a codebase your developers actually enjoy maintaining. (devblogs.microsoft.com)

30-day .NET 10 upgrade checklist on sticky notes