# 2023 R2 gRPC Interface-Version Integers (C3a)

**Captured:** 2026-06-25  
**Transport:** 2023 R2 gRPC (h2c, unauthenticated `GetInterfaceVersion` RPCs — no credentials required)  
**Status:** LIVE — integers captured from a real AVEVA Historian 2023 R2 server.

## Captured Values

| Service        | UiVersion / Version | UiError / Error | Notes                                              |
|---------------|---------------------|-----------------|----------------------------------------------------|
| History        | 12                  | 0               | Matches `HistoryInterfaceVersionGrpc2023R2 = 12`   |
| Retrieval      | 4                   | 0               | Matches `RetrievalInterfaceVersion = 4` (unchanged from 2020) |
| Transaction    | 2                   | 0               | Matches `TransactionInterfaceVersion = 2` (unchanged from 2020) |
| Status         | 4                   | 0               | Reachability-only; version integer is not version-gated (see note) |

> **Field-name note:** The History, Retrieval, and Status proto responses use `UiError`/`UiVersion` fields.
> The Transaction response uses `Error`/`Version` (different naming convention in the proto). Both are
> captured correctly; the table uses a unified column header for readability.

> **Status note:** `StatusService.GetStatusInterfaceVersion` returned UiVersion=4, UiError=0 on the live
> 2023 R2 server. Status is classified as reachability-only — its version integer carries no semantic
> meaning for the SDK's byte serializers — so its UiVersion is not gated and not asserted in tests.

## Evidence Test

`tests/AVEVA.Historian.Client.Tests/GrpcInterfaceVersionEvidenceTests.cs` —
`GrpcInterfaceVersions_LiveServer_MatchAcceptedSet` reads these four RPCs live and asserts:
- `history.UiError == 0` and `history.UiVersion ∈ {11, 12}`
- `retrieval.UiError == 0` and `retrieval.UiVersion == 4`
- `transaction.Error == 0` and `transaction.Version == 2`
- `status.UiError == 0` (version not asserted)

The test skips silently when `HISTORIAN_GRPC_HOST` is absent.

## Gap Closed

This document closes the **C3a** gap: "2023 R2 gRPC server-version integers not yet captured."
Prior to this capture, the `HistorianServerVersionGate` accepted History=12, Retrieval=4, and
Transaction=2 on the basis that they were inferred/expected-to-be-unchanged. All four integers are
now confirmed from a live 2023 R2 server over the gRPC transport; no widening of `AcceptedVersions`
is required (all captured values were already accepted).

The 2020 WCF baseline (History=11, Retrieval=4, Transaction=2) was captured earlier via the
`wcf-probe` command and is documented in `wcf-probe-remote-latest.json` and `wcf-contract-evidence.md`.