.NET 10 LTS is out, and the clock is already ticking. For most production teams, a .NET 10 LTS upgrade is the smartest way to lock in three full years of patches while picking up performance gains, tighter security defaults, and a cleaner developer experience. This guide gives you the dates that matter, the pitfalls to watch, and a field-tested 30‑day plan to ship your .NET 10 LTS upgrade without burning a quarter on yak‑shaving.
What just shipped—and why it matters
.NET 10 released on November 11, 2025 as a Long‑Term Support (LTS) version with support through mid‑November 2028. Visual Studio 2026 shipped alongside, so if you live in Microsoft’s IDE, you’ll want that update to get first‑class C# 14 support, updated analyzers, and a smoother target‑framework story. If you’ve been on .NET 8 (LTS) or .NET 9 (STS), note this: both .NET 8 and .NET 9 reach end of support on November 10, 2026. That gives you about a year to upgrade and stabilize before the older stacks age out.
On the web stack, ASP.NET Core 10 brings security and ergonomics you can feel: OpenAPI 3.1 by default, Identity support for passkeys (WebAuthn/FIDO2), better diagnostics, and memory optimizations that reduce long‑running app footprints. On the runtime side, NativeAOT continues to mature, the JIT shaved cycles across codegen and vectorization paths, and the base class libraries expanded with practical APIs like WebSocketStream, async ZipArchive operations, and stricter JSON handling (disallow duplicate properties). If you care about cryptography planning, .NET 10 also expands post‑quantum options so you can start modeling future‑proof key exchanges.
Primary benefits you can defend at the planning meeting
Here’s the thing: upgrades compete with revenue work. You need a defensible list of wins.
Performance: Microsoft’s yearly perf sweeps keep finding headroom. In real apps, that translates to lower p95 latencies and fewer pods to meet SLOs. Even if you never touch a new keyword, the runtime and BCL improvements show up across serialization, networking, and allocation‑hot paths.
Security posture: Passkeys enable phishing‑resistant login flows; JSON duplicate‑property rejection reduces a whole class of tricky deserialization bugs; expanded PQC support helps you explore hybrid cryptosystems where that matters (regulated workloads, long‑lived secrets).
Developer experience: C# 14 extension members reduce boilerplate in shared libraries, field‑backed properties make refactors safer, and implicit Span conversions play nicely with high‑performance APIs. Add modern OpenAPI defaults and better minimal‑API validation, and you save hours on glue code.
Support runway: Executives like dates. .NET 10 LTS gives you three years of updates. Align your compliance and platform lifecycle to that calendar and avoid emergency scrambles in late 2026.
Headline changes that may break or surprise you
OpenAPI 3.1 as the default: If your tooling expects 3.0, you’ll see differences (nullable types, JSON Schema 2020‑12). Adjust your generators or pin 3.0 in configuration. This change is great long‑term but can nudge CI pipelines on day one.
Identity and passkeys: Enabling passkeys requires correct Relying Party IDs and TLS. Expect to thread changes through your UX, recovery flows, and device‑binding policies. It’s worth it, but plan QA across browsers and mobile platforms.
Container base images moved: Starting with .NET 10, default Linux tags now use Ubuntu 24.04. Most apps won’t notice, but custom native dependencies and package installs might. Also confirm your orchestrator node pools have the right base image support.
Minimal API validation: Built‑in validation is a win, but in legacy code that manually validates, you can double‑fail requests or return unexpected 400s. Decide if you’ll lean on the framework behavior or keep custom validators—and be consistent.
JSON strictness: Disallowing duplicate properties closes off ambiguous payloads. That’s good security hygiene, but clients with sloppy serializers may suddenly fail. Call it out in your API change log.
Why a .NET 10 LTS upgrade makes sense right now
Two forces align in 2025–2026: you get an LTS foundation with tangible runtime and web‑stack gains, and you’re staring down a synchronized end‑of‑support window for both .NET 8 and 9 in November 2026. Upgrading this quarter creates breathing room to finish migrations, settle performance, and handle remaining library upgrades before peak season next year. If you’re weighing the move, our deeper dives on why .NET 10 LTS is worth the upgrade now and what .NET 10 LTS changes for your web stack can help you make the case with stakeholders.
C# 14: the two features your team will actually use
Extension members: They turn the old “one extension method per type per file” sprawl into tidy extension blocks, and they unlock extension properties and static members. Perfect for infrastructure libraries where you don’t own the types.
Field‑backed properties: A smooth path off auto‑props without rewriting call sites. You’ll use this the first time you add trimming or normalization logic to a hot model type.
Honorable mentions: implicit span conversions, null‑conditional assignment, and partial constructors/events. None are flashy—and that’s a compliment. They read like features built by people who ship large codebases.
The 30‑day .NET 10 LTS upgrade playbook
Days 1–5: Inventory and blast radius
Map every app and service targeting .NET 6–9. For each, record: target framework, hosting model (IIS/Kestrel/reverse proxy), containerization status, OS base images, CI/CD lane, and critical libraries (Auth, EF Core, Serilog, Polly, OpenTelemetry, Swashbuckle/NSwag/Scalar, caching). Tag owners and SLOs.
Decide your toolchain baseline: Visual Studio 2026 on Windows; the .NET 10 SDK for CI; update VS Code extensions if that’s your flow. Align analyzers and code‑style rules across repos to avoid churn.
Days 6–14: Proofs, pins, and package strategy
Pick a non‑critical API and a background worker as upgrade pilots. Bump TFM to net10.0, enable C# 14, and flip ASP.NET Core OpenAPI to 3.1. Confirm your doc generation and client SDK pipelines still produce the expected outputs. Where you have generators, pin their versions so you don’t fight two fronts.
Containers: Move SDK/runtime tags to 10.0 and validate Ubuntu‑based images. Keep a parallel branch with your previous base image for rollback. Verify health probes, port mappings (remember many official ASP.NET images default to port 8080), and that your OpenTelemetry and metrics exporters still scrape correctly.
Security: Pilot passkeys in a sandbox environment. Validate RPID, origin checks, and device recovery UX. Sketch the comms plan—users will have questions.
Days 15–25: Scale out and tighten the screws
Roll the upgrade to 20–30% of your services. Watch p95 latency, memory steady‑state, GC pauses, and CPU across business‑as‑usual traffic. NativeAOT candidate? Try it on one console tool, not your main API. Tighten logging to catch 400s that new validation rules surface. If your APIs receive third‑party traffic, announce the JSON duplicate‑property behavior now.
Refactor opportunities: Replace glue code where C# 14 gives you cleaner patterns (extension blocks around core primitives; field‑backed properties on DTOs with normalization). These are small, high‑leverage changes that pay down debt while you’re already touching the code.
Days 26–30: Formalize and lock
Capture your upgrade runbook in the repo wiki: TFM changes, analyzers, OpenAPI settings, container tags, passkey decisions, and rollback procedures. Set organization‑wide SDK pins to 10.x in global.json to prevent accidental downgrades in CI. Cut a minor version of your services and publish a change log that calls out OpenAPI and JSON changes specifically.
People also ask
Should we skip .NET 9 and go straight to .NET 10 LTS?
Yes, if you’re on .NET 8 or earlier. With .NET 9’s STS now at 24 months and both .NET 8 and 9 ending support on November 10, 2026, .NET 10 LTS buys you stability through 2028 with better performance and a modern web stack.
Do we need Visual Studio 2026 to target .NET 10?
For Windows shops on Visual Studio, yes—use Visual Studio 2026 for first‑class .NET 10 and C# 14 support. On Linux/macOS, the .NET 10 SDK plus your editor of choice (e.g., VS Code) is sufficient.
Will OpenAPI 3.1 break our clients?
It won’t “break” well‑behaved clients, but small schema differences (especially nullability) can ripple through codegen. If you’re mid‑contract with partners, consider pinning generator pipelines or exposing both 3.0 and 3.1 during a transition window.
Is C# 14 required after we upgrade?
No. You can compile existing C# without adopting new syntax. It’s worth enabling C# 14 to unlock analyzers and small ergonomics wins, but you can stage that separately from the runtime upgrade.
Concrete checks before you flip the switch
— Verify your container base images: moving from Debian to Ubuntu on the default tags can change package names and minor libc behavior. If you install native dependencies, test image builds in CI rather than discovering it at deploy time.
— Align OpenAPI: make an explicit decision on 3.1 vs 3.0. If you’re staying on 3.0 for now, set it in code or MSBuild so a future SDK update doesn’t surprise you.
— Decide on minimal‑API validation: embrace the framework behavior across your endpoints or disable it where you have custom validators. Avoid mixed patterns.
— Plan passkey rollout: start with staff accounts or a limited customer cohort. Update support docs before enabling it broadly.
— Update analyzers and code‑style: new language features can trigger lints. Tweak rulesets so CI failures are signal, not noise.
Version numbers and dates that matter
— .NET 10 LTS released: November 11, 2025. Support through mid‑November 2028.
— .NET 8 (LTS) and .NET 9 (STS) end of support: November 10, 2026.
— Visual Studio 2026: current release with .NET 10/C# 14 support.
— Docker images: mcr.microsoft.com/dotnet/aspnet:10.0 and mcr.microsoft.com/dotnet/sdk:10.0 now default to Ubuntu 24.04 for Linux tags that don’t specify an OS.
— Web stack highlights: ASP.NET Core 10 defaults to OpenAPI 3.1, Identity adds passkey support, diagnostics and memory reuse are improved, and System.Text.Json tightens input handling.
Let’s get practical: a migration framework you can reuse
I coach teams to apply the same five steps to every platform upgrade: 1) inventory and owners, 2) baselines and pins, 3) one pilot per workload type, 4) scale with guardrails, 5) lock and document. The 30‑day plan above implements that. If you want a longer cut with example checklists and dependency heat maps, see our take on shipping on .NET 10 LTS. If your org is planning a 2026 modernization wave, pair this with our .NET 10 LTS reality check for 2026 upgrades to avoid surprise scope creep.
Risks, limits, and edge cases
Legacy ASP.NET Core 2.x/3.x libraries and middlewares that weren’t maintained may block the move—especially anything that hooked deep into request parsing, JSON, or OpenAPI generation. EF Core upgrades can surface subtle query changes or migrations that need careful review. If you run on-prem with strict FIPS or custom cryptography, test the new crypto defaults and PQC APIs in a staging environment; don’t flip those in prod just because they’re available.
Also, watch your third‑party OpenAPI tooling. If a vendor tool hard‑codes 3.0 assumptions, either pin your server to 3.0 for now or keep a compatibility endpoint that serves 3.0 while most clients move to 3.1.
What to do next
— Book two developer weeks to run the 30‑day plan on a pilot service and a worker.
— Standardize SDK 10.x in global.json, update Visual Studio/CI images, and freeze generator versions.
— Decide OpenAPI 3.1 vs 3.0, publish the decision, and update client SDK pipelines.
— Trial passkeys with a small user slice and capture support feedback before a broad rollout.
— Set a firm “code stop” date for .NET 8/9 features and start funneling new work onto .NET 10. Need a partner? Explore how we run these engagements on our services page or get in touch.
Zooming out
You don’t need to refactor everything to get value from .NET 10 LTS. Take the runtime wins, fix the one or two places where defaults changed under you, and ship. Then, layer in C# 14 ergonomics and passkeys at a deliberate pace. That balance—fast upgrade, selective adoption—lets you bank the benefits now and keep momentum for the rest of your roadmap.
If this resonated and you want more hands‑on tactics, our blog has field notes on adjacent platform moves—from Next.js 16 caching and proxying strategies to keeping CI sane during security and billing shifts. We build for the long term; we’d love to help you do the same.
