.NET 10 LTS is out, with three years of long‑term support through November 2028. That matters. You get a stable runtime, a modern language bump with C# 14, meaningful ASP.NET Core and EF Core 10 improvements, and performance wins you can feel in production. This isn’t a marketing refresh; it’s a release that changes how you structure APIs, model data (including vectors), and secure your edge.
Why .NET 10 LTS matters right now
Every upgrade pitch says “faster and more secure.” Here’s the thing: with .NET 10 LTS you also get platform stability through 2028, new language features that reduce boilerplate, and data capabilities that cut infrastructure sprawl. If you’re running APIs behind a gateway, experimenting with AI‑adjacent features, or pushing for lower cloud spend, this release hits your goals on three fronts—developer velocity, runtime performance, and data architecture.
For engineering leaders, the timing is practical. Many companies deferred big platform moves in 2024–2025 while shipping features. LTS buys you a safe consolidation window for 2026 roadmaps. For developers, C# 14’s ergonomics and ASP.NET Core template updates clear away persistent papercuts. And for data teams, EF Core 10’s alignment with SQL Server 2025 and Azure SQL (native JSON and vector support) lets you ship retrieval‑augmented features or smarter recommendations without adding yet another database.
What’s actually new that changes your day‑to‑day
C# 14: fewer footguns, less boilerplate, real expressiveness
C# 14 isn’t flash for its own sake. The new extension members make it natural to add domain‑specific capabilities to types you don’t own—even static extension members—so you stop littering helpers across projects. Field‑backed properties give you the cleanliness of auto‑properties with just enough room for guard logic. You’ll also notice smoother work with spans (implicit conversions), null‑conditional assignment for tidy null‑safe updates, lambdas that support parameter modifiers without verbose type noise, and better partial members that play nicely with source generators.
Net effect: slightly smaller diffs, fewer custom backing fields, and fewer utility classes. You’ll feel it most in shared libraries and performance‑sensitive code, where span ergonomics reduce friction without sacrificing safety.
ASP.NET Core: OpenAPI defaults, better JS interop, clearer docs flow
The Web API (Native AOT) template now includes OpenAPI generation by default, and the platform exposes an injectable OpenAPI document provider. That means you can generate or inspect your API contract from background jobs or during startup—not just at request time. It’s a small shift with big payoffs for CI, contract tests, and schema linting. JavaScript interop in Blazor also gets more predictable with constructor invocation and property access helpers, which trims the glue code when you wrap third‑party widgets or charting libraries.
Documentation generation gets smarter too. XML doc handling is less brittle with complex types, lowering random build breaks. It’s the unsexy work that moves teams faster during release crunches.
EF Core 10 + SQL Server 2025/Azure SQL: native JSON and vector search
This is the sleeper feature set that changes app design. With SQL Server 2025 and Azure SQL you get a native JSON type, plus vector storage and distance functions. EF Core 10 meets the database where it is: map JSON columns without stringly‑typed hacks, and use EF.Functions.VectorDistance() to build similarity queries for recommendations, semantic search, or categorization—all from your existing relational store. You keep ACID, governance, and backup policies intact while layering in modern retrieval patterns.
If you’ve been piloting a separate vector database or juggling JSON in NVARCHAR columns, this simplifies your stack and your cost model. The practical catch is deployment: run on SQL Server 2025 (compat level 170+) or current Azure SQL; update drivers; and test your query shapes under production‑like load. Done right, this is a net reduction in moving parts.
Security first: patch the Kestrel issue before you celebrate
In October 2025 Microsoft shipped a critical fix for an HTTP request smuggling vulnerability in Kestrel. If you maintain ASP.NET Core apps (including those you’ll move to .NET 10 LTS), make sure your runtime and hosting bundle are patched and your processes restarted. Teams sometimes update SDKs but forget to roll the patched runtime to app servers or containers. Don’t be that team; bake a runtime check into your health endpoints and CI images, and re‑deploy with a clean restart to load the fixed binaries.
If you front Kestrel with a reverse proxy, you still patch. Proxies mitigate some smuggling vectors, but your risk depends on how request boundaries are interpreted through the chain. Update first; argue about theory later.
A pragmatic .NET 10 LTS upgrade plan (6 steps)
Let’s get practical. This is the sequence we use with client teams to move production services without drama.
1) Inventory and de‑risk dependencies
Run dotnet list package --outdated across your solution and snapshot the output. Flag packages with source generators, analyzers, or custom MSBuild props—they’re the usual sources of pain. For web projects, note auth libraries, OpenAPI generators, and JSON serializers. If you’re using EF Core, list providers and any raw ADO.NET usage. Create a three‑tier map: must‑upgrade, likely OK, unknown. Resolve the unknowns first.
2) Update CI images and developer environments
Pin your build agents and container images to the .NET 10 SDK and the matching runtime. Don’t mix “new SDK, old runtime” in production hopes. If you deploy to Windows hosts, install the hosting bundle on stage and prod; for Linux containers, retag your base images and re‑publish. Add a runtime version check to your startup logs so ops can confirm what’s actually running.
3) Target net10.0 and adopt C# 14 intentionally
Bump your Target Framework to net10.0. For language versioning, either set C# 14 explicitly or rely on the SDK default. Decide as a team which C# 14 features you’ll use immediately (field‑backed properties and null‑conditional assignment are easy wins) and which you’ll defer to avoid noisy diffs. Establish a short guideline in your repo wiki to keep code reviews predictable.
4) Modernize ASP.NET Core templates and OpenAPI
Regenerate a fresh Web API (Native AOT) sample and compare Program.cs, logging, and OpenAPI setup with your current projects. Move to the new defaults where sensible, especially the integrated OpenAPI document provider if you generate contracts in CI. If you previously relied on automatic cookie redirects in API endpoints, verify you’re returning clean 401/403 responses instead of HTML redirects; adjust middleware ordering and auth attributes accordingly.
5) Upgrade EF Core and lean into JSON + vectors
Move to EF Core 10 and test against SQL Server 2025 or current Azure SQL. Migrations that add JSON columns should use the native type; measure storage and query plans versus prior NVARCHAR implementations. For vector workloads, wire up embeddings, store in VECTOR columns, and query with cosine or dot‑product distance depending on normalization. Validate your LINQ translates to expected SQL with a logger; pre‑compute norms if you care about absolute throughput. Update your data drivers to current versions that know about JSON and VECTOR types.
6) Prove it: performance profiles and safe rollout
Benchmark microservices under production‑like load. Focus on cold start (NativeAOT where feasible), steady‑state throughput, allocs per request, and GC pauses. Capture before/after numbers in a single Markdown doc to justify the upgrade to finance and leadership. Roll out with a canary: 5% traffic for 24 hours, then ramp to 25%, then full—watch error budgets and latency percentiles. Feature flags are your friend.
People also ask
Should we move from .NET 8 to .NET 10 LTS now or wait?
If you’re on .NET 8 LTS and shipping comfortably, there’s no emergency. But you also don’t want a pile‑up in late 2026. Plan the transition in Q1–Q2 2026: patch security issues now, align your CI images, and start porting lower‑risk services. If you’re on .NET 7 or earlier, you’re already outside mainstream support; prioritize the move sooner.
Do we need SQL Server 2025 to use EF Core 10?
No—EF Core 10 runs on .NET 10 and works with earlier engines. You only need SQL Server 2025 (or current Azure SQL) for the native JSON type and vector columns. If those features are part of your 2026 roadmap (think semantic search or complex JSON payloads), align your database upgrade now and test providers and drivers together.
Is C# 14 required, and will it break builds?
C# 14 is available with .NET 10 but doesn’t force you to use new syntax. Most teams adopt it gradually. The build breaks we see are rarely the language—more often analyzers, source generators, or old MSBuild props. Keep language adoption intentional, with a short checklist of allowed patterns in your first sprint after the upgrade.
Risks, tradeoffs, and gotchas
Every LTS jump carries risk. Security fixes require runtime redeploys, not just SDK updates. Native AOT isn’t free—some reflection‑heavy libraries won’t trim well; you’ll need to annotate or exclude paths. OpenAPI defaults are great, but if you’ve generated client SDKs from custom pipeline steps, the new DI‑friendly provider can change how you surface docs in CI; test that contract. EF Core’s JSON and vector support is powerful, but query shapes and indexes still matter; measure distance functions under real load and choose metrics wisely. Finally, don’t assume your gateway fully neutralizes request‑smuggling patterns. Patch first, design defense‑in‑depth second.
Use this 30‑minute readiness checklist
Print this, or paste it in your sprint board:
- Runtime patched and restarted on all app hosts and containers; health endpoint reports exact runtime version.
- Build agents and base images pinned to .NET 10 SDK and runtime; no drift between CI and prod.
- Solution compiles under
net10.0; analyzers and source generators updated or disabled with justification. - Auth flows verified: APIs return 401/403; no unexpected redirects; OpenAPI doc builds in CI from DI provider.
- EF Core updated; database engine validated; JSON and vector features tested where applicable; drivers updated.
- Performance baselines captured; canary plan written (percentages, metrics, rollback conditions).
What to do next
Want a deeper dive on planning the move? Start with our take on what .NET 10 LTS actually changes for your web stack, and then weigh the ROI in why the upgrade is worth it right now. If you’re ready to execute, grab our ship‑week checklist for .NET 10 LTS and pressure‑test your 2026 plan with the reality check for large‑scale upgrades.
If your team needs a partner to accelerate the migration, see our services and bring us in for a two‑week spike: we’ll blueprint your path, de‑risk the hard parts, and hand you benchmarks your leadership cares about.
