Voltrus Gateway vs Kepware: A Cross-Platform OPC Gateway Alternative
If you're shopping for an industrial protocol gateway, Kepware (KepserverEX) is the name everyone knows. It's the default OPC server in countless plants. But it carries assumptions that are increasingly awkward in 2026: it's Windows-only, it's licensed per instance and often per tag, and it speaks OPC as its primary surface — not a modern typed API your application code actually wants to call.
This is an honest comparison of Voltrus Gateway against Kepware across the dimensions that matter when you're building a data-collection layer, an edge collector, or a SCADA backend: platform coverage, protocol breadth, the API surface, licensing model, and total cost.
Platform Coverage: Cross-Platform vs Windows-Only
Kepware is a Windows application. It runs on Windows Server (and desktop Windows for development). To deploy it at the edge — on a Linux gateway box, in a container, beside a PLC on the shop floor — you're carrying a Windows license and Windows operational overhead.
Voltrus Gateway is a single static Rust binary. The same file runs on Linux (x86_64 and aarch64), macOS (Apple Silicon and Intel), and Windows. Drop it in a Docker container, run it on a Raspberry Pi, or put it on a Windows server — it's one binary with no runtime dependencies. For edge and cloud-native deployments, that's the difference between "a service" and "a Windows VM we have to patch."
Protocol Breadth: Six Protocols, One API
Kepware supports many protocols through purchased drivers — each driver is a separate line item. Voltrus Gateway ships Modbus TCP, OPC UA, EtherNet/IP (CIP), Siemens S7, DNP3, and BACnet/IP all in the one binary, each with full read, write, and subscribe support, behind a single gRPC surface. You don't pick drivers; you pick a protocol in the connect call.
The API Surface: Typed gRPC vs OPC + COM
This is the biggest architectural difference. Kepware's primary client surface is OPC (DA, UA) and its legacy COM/DA interface. To read a tag from your application you go through an OPC client library, or through Kepware's REST/IoT Gateway — an add-on.
Voltrus Gateway exposes a typed gRPC API directly: OpenSession, ReadTags, WriteTag, SubscribeTags (server-streamed), and Discover. Your application calls one client regardless of the underlying protocol. Tag values are carried as a typed oneof — bool, int32, int64, uint32, float, double, string, bytes — plus a source type, so a CIP DINT or an OPC UA string round-trips intact instead of being flattened to a number.
Licensing: One-Time per Host vs Per-Instance + Drivers + Add-ons
Kepware's licensing stacks: a base server license, drivers (some bundled, some purchased), and add-ons like the IoT Gateway or Redundancy. Tag-count tiers push larger deployments into more expensive editions.
Voltrus Gateway is one-time per host. One license covers one machine running the binary — no per-tag metering, no driver line items, no subscription. Buy it once, run it forever on that host. Deploy on as many hosts as you license.
Comparison Table
| Dimension | Voltrus Gateway | Kepware (KepserverEX) |
|---|---|---|
| Platform | Linux, macOS, Windows — one static binary | Windows only |
| Protocols | Modbus, OPC UA, EtherNet/IP, S7, DNP3, BACnet — all included | Per-driver; some purchased separately |
| Client API | Typed gRPC (read/write/subscribe/discover) | OPC DA/UA + COM; REST via IoT Gateway add-on |
| Subscriptions | Native server-streamed gRPC | OPC subscriptions |
| Type handling | Type-preserving oneof + source type | OPC type system |
| Licensing | One-time, per host, no per-tag | Per instance + drivers + add-ons; tag tiers |
| Edge fit | Container, Pi, edge box — no OS license | Requires Windows at the edge |
When Kepware Still Wins
Kepware isn't wrong for every shop. It wins when you're already a Windows-only plant with OPC as your integration standard, you need a specific niche driver Voltrus Gateway doesn't ship yet, or you depend on Kepware's mature ecosystem of certified drivers and tooling. If your SCADA already speaks OPC and you have a Windows operations team, Kepware is a known quantity.
When Voltrus Gateway Wins
Voltrus Gateway wins when you're building new software on top of your PLC data — a custom collector, a cloud pipeline, an edge service — and you want a modern typed API your code can call directly, without an OPC client library in the middle. It wins at the edge (Linux/container), and it wins on licensing simplicity for teams that don't want to track driver SKUs and tag tiers.
One gRPC API for Every Protocol
Voltrus Gateway unifies Modbus, OPC UA, EtherNet/IP, S7, DNP3, and BACnet/IP behind a single typed gRPC surface. Cross-platform, self-hosted, one-time per host.
Explore Voltrus Gateway →The Bottom Line
Kepware is a Windows OPC server with a per-driver, per-tag licensing model. Voltrus Gateway is a cross-platform Rust binary with a typed gRPC API and one-time per-host licensing. They overlap on "talk to industrial devices" but differ sharply on platform, API ergonomics, and cost structure. If your application wants to call a typed streaming API — not an OPC client — Voltrus Gateway is the modern alternative.