.NET 10 LTS landed on November 11, 2025, and it already has its first servicing update (10.0.1 on December 9). For most web teams, this is the moment to schedule the jump: longer support, measurable performance wins, and fixes you want in production. If you own ASP.NET Core APIs or Blazor apps, the question isn’t “if,” it’s “how quickly can we upgrade without drama?” (dotnet.microsoft.com)
Why .NET 10 LTS matters now
LTS means three years of support. In practice, that’s budget clarity, fewer emergency change windows, and a predictable patch rhythm. Microsoft’s support table lists .NET 10 as LTS with 10.0.1 shipped December 9, 2025—useful if your security team asks for the latest patch level during change control. (dotnet.microsoft.com)
There’s also momentum. The official announcement and .NET Conf 2025 sessions emphasize performance, security hardening, and developer quality‑of‑life improvements—exactly what you want from a long‑term base. (devblogs.microsoft.com)
What’s actually new in .NET 10 LTS (and worth your time)
Here’s the thing: not every shiny bullet point moves real workloads. These do.
C# 14: small changes, big ergonomics
C# 14 brings extension members, null‑conditional assignment, field‑backed properties, partial events/constructors, and more Span conversions. These features aren’t hype; they trim boilerplate and reduce allocation footguns in hot paths. (learn.microsoft.com)
ASP.NET Core 10: security, observability, and cleaner APIs
Microsoft calls out a few upgrades that matter in production:
• OpenAPI 3.1 by default with improved JSON Schema alignment—less generator friction and cleaner client contracts.
• New authentication/authorization metrics and better diagnostics—finally, visibility for the stuff that actually breaks prod.
• Built‑in Server‑Sent Events via TypedResults.ServerSentEvents() for real‑time UX without yak‑shaving middleware.
• Passkey (WebAuthn/FIDO2) support in ASP.NET Core Identity and Blazor templates—passwordless flows with fewer knobs. (devblogs.microsoft.com)
Operationally, automatic memory‑pool eviction reduces long‑running app bloat, lowering noisy neighbor effects on shared nodes. It’s one of those fixes you notice when your 90th percentile latency mysteriously stabilizes after a week. (devblogs.microsoft.com)
EF Core 10: vectors and modern SQL features
EF Core 10 is LTS and requires .NET 10. It adds first‑class support for vector data and VECTOR_DISTANCE() on Azure SQL Database and SQL Server 2025—useful if you’re building semantic search or RAG features inside your transactional systems. If you’ve been stashing embeddings in a sidecar store, this lets you consolidate reads and transactions where it makes sense. (learn.microsoft.com)
We’ve been helping teams weigh vector storage options across cloud services; if you’re on AWS, compare EF’s SQL vectors with the approach in our pragmatic build guide for S3 Vectors GA. See the S3 Vectors GA build guide to understand trade‑offs in latency, cost, and ops before you pick your long‑term home for embeddings.
Runtime and crypto: tangible performance and PQC
.NET 10 claims measurable runtime gains (JIT, GC, NativeAOT). On supported hardware you also get AVX10.2 and Arm64 SVE optimizations. For security roadmaps, new APIs expose post‑quantum cryptography (ML‑KEM, ML‑DSA, SLH‑DSA) and add a WebSocketStream for stream‑first designs. These are forward‑looking but already useful for long‑lived apps. (visualstudiomagazine.com)
Security watch: Kestrel request‑smuggling (CVE‑2025‑55315)
In October, Microsoft patched an HTTP request‑smuggling vulnerability in Kestrel with a 9.9 CVSS score—described by Microsoft staff as their “highest ever” for ASP.NET Core. If your app proxy chain or header parsing is quirky, this could bypass auth and leak credentials. Treat it as a must‑verify item before or during your .NET 10 migration. (infoq.com)
What should you check?
• Confirm you’re on patched builds: .NET 10 RTM and later include the fix; older 8/9 lines also have patched updates. Verify your exact runtime package versions in CI/CD and containers.
• Scan for compatibility flags: Microsoft introduced a temporary rollback switch around chunked‑encoding parsing. If you used it as a crutch during October triage, remove it before go‑live. (github.com)
Signal to your stakeholders: the risk here is architecture‑dependent. The public score is 9.9, but the exploitability varies with your proxies and code paths. Still, don’t rely on luck—patch and validate. (infoq.com)
.NET 10 LTS upgrade plan: 30 days, zero drama
This is the rollout we use with product teams that deploy weekly and can afford a single rehearsal on staging. Adapt the calendar to your release cadence.
Days 1–2: inventory and blast radius
• Enumerate all .NET runtimes and ASP.NET Core versions across services and jobs. Include container base images and self‑contained deployments.
• Map dependency hotspots: EF Core, third‑party middleware, OpenAPI tooling, and any codegen clients.
• Note security posture: verify patched Kestrel builds are available in your repos and images. (dotnet.microsoft.com)
Days 3–5: toolchain and CI
• Install SDK 10.x locally and in CI, alongside your existing SDKs.
• Pin Visual Studio 2026 or VS Code C# Dev Kit to match; set a feature branch policy that builds against SDK 10.
• Add a matrix job that compiles on .NET 10 without publishing artifacts; collect warnings as errors to flush breaking changes early. (devblogs.microsoft.com)
Days 6–10: compile and smoke test
• Update TargetFramework to net10.0 for one representative service (ideally an internal API).
• Replace custom or legacy OpenAPI shims with out‑of‑the‑box 3.1 generation; regenerate clients and run request‑replay tests.
• Turn on new auth/identity metrics; ensure dashboards and alerts exist for login failures and token refresh rates. (infoq.com)
Days 11–15: performance budget
• Benchmark hot endpoints with your real traffic shape. Record p50/p90 latency, CPU per request, and memory working set.
• Enable NativeAOT for small console tools or gRPC utilities where cold‑start matters.
• Observe memory‑pool eviction behavior during overnight idle periods; verify container memory limits don’t thrash. (visualstudiomagazine.com)
Days 16–20: data layer and vectors
• Move one service to EF Core 10; run storage‑engine‑specific tests (query plans, timeouts, connection pool behavior).
• If you plan semantic search, prototype vector columns and measure write amp, index size, and ANN latency against your current vector store. Use production‑like embeddings (dimension, distribution) to avoid demo‑only results. (learn.microsoft.com)
Thinking about broader vector infrastructure? Our build‑versus‑buy deep‑dive on S3 Vectors lays out costs and traps before you commit. Read the buy‑or‑build guide for vectors.
Days 21–25: security rehearsal
• Re‑run your HTTP smuggling tests: mismatched Content‑Length and Transfer‑Encoding headers, odd chunk extensions, and edge proxy desync cases.
• Validate passkey flows end‑to‑end, including recovery and device upgrade scenarios; add strong telemetry around WebAuthn errors.
• Confirm that OpenAPI 3.1 docs reflect your auth requirements correctly; break glass if a generator change would ship an insecure client. (devblogs.microsoft.com)
Days 26–30: rollout
• Ship to a canary slice with feature flags for passkeys and SSE endpoints.
• Monitor login success rate, 401/403 ratios, TLS handshake errors, CPU/memory, and GC pause times.
• Publish a change advisory with the .NET 10 LTS baseline and patch level. Include rollback criteria tied to user‑visible SLOs. (dotnet.microsoft.com)
Gotchas we’ve already seen
• OpenAPI surprises: moving to 3.1 can break custom transformers or client codegen that expected 3.0 semantics. Budget half a day to review diffs and regenerate clients.
• Cookie auth behavior: endpoints that used to redirect might now return 401/403; update front‑end error handling and UI flows.
• EF Core breaking edges: complex type mapping and JSON handling may behave differently; add snapshot tests for serialization round‑trips. (infoq.com)
.NET 10 LTS vs. staying on 8 or 9
If you’re on .NET 8 LTS and shipping comfortably, you’re not in a panic. But the math favors moving: three more years from a faster base, built‑in passkeys, better OpenAPI, and EF 10’s vector features. For .NET 9 STS, you have a shorter runway; plan the hop to .NET 10 now to avoid a crunch in late 2026. (dotnet.microsoft.com)
People also ask
Is .NET 10 LTS worth it if I’m on .NET 8?
Yes if you want built‑in passkeys, better OpenAPI, and cleaner observability without bespoke plumbing. If your team is slammed, start with the SDK/CI split build and upgrade the highest‑ROI service first. (devblogs.microsoft.com)
Do I need to recompile everything at once?
No. Multi‑SDK CI is your friend. Prove it on a low‑risk API, then roll through bounded contexts. Keep shared packages dual‑targeted until the fleet catches up.
What IDE supports .NET 10?
Visual Studio 2026 and the updated C# Dev Kit for VS Code. Pin the versions across your team so build diagnostics match what CI sees. (devblogs.microsoft.com)
Will the Kestrel CVE hit me if I’m behind a reverse proxy?
Maybe. Reverse proxies mitigate many cases, but desync between proxy and Kestrel is exactly how request smuggling works. Patch, then test the odd cases deliberately. (infoq.com)
Let’s get practical: a pre‑flight checklist
• Confirm support horizon: .NET 10 LTS and 10.0.1 in all environments (dev, CI, staging, prod).
• Enable new ASP.NET Core metrics; wire into dashboards before rollout.
• Regenerate OpenAPI docs and clients; run compatibility tests.
• Patch and validate for CVE‑2025‑55315; remove temporary flags.
• Decide now whether vectors live in SQL (EF 10) or a dedicated store; don’t split reads casually. (dotnet.microsoft.com)
Zooming out: architecture choices this release nudges
.NET 10 LTS nudges teams toward simpler stacks: fewer hand‑rolled auth flows thanks to passkeys, fewer out‑of‑tree OpenAPI tweaks, and better built‑ins for diagnostics. If you’ve been nursing a custom JSON Patch or SSE implementation, retire it. And if your org is laying AI plumbing, EF 10’s vector support means you can keep more logic in your primary DB—though we still advise testing retrieval latency against dedicated vector services before committing at scale. (devblogs.microsoft.com)
Related playbooks and security guides
Running a mixed JavaScript/.NET shop? Our zero‑drama Node.js 24 LTS plan pairs nicely with this timeline. If you maintain React or Next.js front ends, keep an eye on recent vulns and patch hygiene: see our Next.js CVE‑2025‑66478 guide and the React2Shell patch playbook for concrete rollout steps that match the approach here.
What to do next
• Book the 30‑day window and name an owner.
• Stand up multi‑SDK CI and build a canary with net10.0.
• Regenerate OpenAPI, enable metrics, and baseline performance.
• Patch for the Kestrel CVE and run request‑smuggling tests.
• Decide your vector strategy (EF 10 in SQL vs. an external store).
• If you want a second set of eyes, contact our team—we’ll review your plan and de‑risk the rollout.
