EUAIActClassifier 0.0.1

EU AI Act Classifier

A drop-in middleware for Microsoft.Extensions.AI.IChatClient that classifies every chat conversation against the EU AI Act risk tiers and attaches the result to the response — so you can see, log, or gate on the risk level of what your AI is being asked to do.

It plugs into the standard IChatClient pipeline, works with any provider (OpenAI, Azure OpenAI, Bedrock, …), and supports both streaming and non-streaming calls.

How it works

The middleware passes your request straight through to the underlying model, then makes a second, structured-output call that classifies the whole conversation (your request and the model's reply) into one risk tier. The verdict is attached to the response and read back via response.EUAIActClassification.

   ┌──────────┐   request    ┌────────────────────────────┐   request    ┌──────────────┐
   │  Caller  │ ───────────▶ │  UseEUAIActClassification  │ ───────────▶ │ inner client │
   │          │ ◀─────────── │        (middleware)        │ ◀─────────── │    (LLM)     │
   └──────────┘  response +  └────────────────────────────┘   response   └──────────────┘
                Classification          │       ▲
                                        │       │  Classification { Risk, Category, Reason }
                                        ▼       │
                              ┌────────────────────────────┐
                              │  classify(request + reply) │   second LLM call, temperature 0,
                              │  → structured output       │   JSON-schema-constrained
                              └────────────────────────────┘

Classification is a best-effort side channel: it never throws into your primary response. If the classifier call fails (or there is nothing to classify), the result is recorded as Risk.Unknown rather than surfacing an error.

Risk tiers

The EU AI Act takes a risk-based approach — the higher the tier, the heavier the obligations, and the fewer systems fall into it:

              /\
             /  \          Unacceptable  —  prohibited outright       (Art. 5)
            /----\
           /      \        High          —  strict obligations  (Art. 6 / Annex III)
          /--------\
         /          \      Limited       —  transparency duties       (Art. 50)
        /------------\
       /              \    Minimal       —  no obligations (the default)
      /----------------\

Every conversation is mapped to one of these tiers (see Risk):

Usage

// Add the classification middleware to any IChatClient pipeline.
var client = openAiClient
    .AsIChatClient()
    .AsBuilder()
    .UseEUAIActClassification()
    .Build();

// Use the client exactly as before.
var response = await client.GetResponseAsync(
    messages:
    [
        new ChatMessage(ChatRole.User, "This is a harmless question: How are you?"),
    ]);

// Read the classification attached to the response.
var classification = response.EUAIActClassification;
Console.WriteLine(classification?.Risk);      // Minimal
Console.WriteLine(classification?.Category);  // e.g. "Minimal risk – general assistance"
Console.WriteLine(classification?.Reason);    // short justification

The same getter works for streaming calls — collect the updates into a response and read it back:

var updates = await client.GetStreamingResponseAsync(messages).ToListAsync();
var risk = updates.ToChatResponse().EUAIActClassification?.Risk;

The result

Classification carries three fields:

Notes

• Classifies the use case, not the topic. A request that merely mentions a sensitive subject stays Minimal if the AI is only acting as a general assistant; the tier reflects the AI system's purpose, as the Act intends.
• Requires a structured-output-capable model for the classification call (it is constrained to a JSON schema and run at temperature = 0 for stability).
• General-purpose AI model obligations (Chapter V) are out of scope — the middleware judges the use-case risk tier of a conversation, not model-provider duties.
• This is a classification aid, not legal advice or a certified compliance assessment.