// the find
OPCFoundation/UA-.NETStandard
OPC Unified Architecture .NET Standard
This is the OPC Foundation's reference .NET implementation of OPC UA, covering client, server, PubSub, GDS and a long list of companion specs for industrial, energy and manufacturing systems. It suits teams building OPC UA clients or servers in .NET who need spec conformance and the reference behaviour, not a thin client library.
The README says the reference server has passed certification through an OPC Foundation test lab and is re-run against the Compliance Test Tool, which makes it the obvious yardstick for interoperability testing. Target coverage is wide (.NET 10, 9, 8 and Framework 4.8), and the server side has source-generated NodeManagers and DataTypes plus Microsoft.Extensions.DependencyInjection hosting, so you don't hand-write the boilerplate for every companion model. The docs folder is thorough for a protocol stack, with a profiles matrix, a migration guide and per-feature pages for subscriptions, sessions, reverse connect and similar topics.
The 2.0 line is breaking, and stable 2.0.0 isn't out yet. The 2.0 packages on nuget.org are previews, and the newer preview builds come from a GitHub Packages feed, which usually needs a token even for public packages. Migrating from 1.5.378 means working through a large API surface; the analyzer and migration skill help with mechanical changes, but the residual manual work is real, and 1.x only gets security and critical fixes. The scope is also a risk in itself. The README lists more than a dozen companion specs and about ten preview package families, so most teams will use a slice, and stability varies by slice. Check each package's status before you depend on it, and benchmark your own load, since the front page makes no throughput claims.