microsoft/semantic-kernel · critical · NotSupportedException

AI Chat Service type '{appConfig.RagConfig.AIChatService}' i

Error message

AI Chat Service type '{appConfig.RagConfig.AIChatService}' is not supported.

What it means

VectorStoreRAG's Program.cs switches on appConfig.RagConfig.AIChatService and only supports 'AzureOpenAI' and 'OpenAI'. Any other value (including null, empty string, or a typo) falls through to the default branch and throws NotSupportedException at application startup.

Source

Thrown at dotnet/samples/Demos/VectorStoreRAG/Program.cs:48

// and add Chat Completion and Text Embedding Generation services.
var kernelBuilder = builder.Services.AddKernel();

switch (appConfig.RagConfig.AIChatService)
{
    case "AzureOpenAI":
        kernelBuilder.AddAzureOpenAIChatCompletion(
            appConfig.AzureOpenAIConfig.ChatDeploymentName,
            appConfig.AzureOpenAIConfig.Endpoint,
            new AzureCliCredential());
        break;
    case "OpenAI":
        kernelBuilder.AddOpenAIChatCompletion(
            appConfig.OpenAIConfig.ModelId,
            appConfig.OpenAIConfig.ApiKey,
            appConfig.OpenAIConfig.OrgId);
        break;
    default:
        throw new NotSupportedException($"AI Chat Service type '{appConfig.RagConfig.AIChatService}' is not supported.");
}

switch (appConfig.RagConfig.AIEmbeddingService)
{
    case "AzureOpenAIEmbeddings":
        builder.Services.AddSingleton<IEmbeddingGenerator>(
            sp => new AzureOpenAIClient(new Uri(appConfig.AzureOpenAIEmbeddingsConfig.Endpoint), new AzureCliCredential())
                .GetEmbeddingClient(appConfig.AzureOpenAIEmbeddingsConfig.DeploymentName)
                .AsIEmbeddingGenerator());
        break;
    case "OpenAIEmbeddings":
        builder.Services.AddSingleton<IEmbeddingGenerator>(
            sp => new OpenAIClient(appConfig.OpenAIEmbeddingsConfig.ApiKey)
                .GetEmbeddingClient(appConfig.OpenAIEmbeddingsConfig.ModelId)
                .AsIEmbeddingGenerator());
        break;
    default:
        throw new NotSupportedException($"AI Embedding Service type '{appConfig.RagConfig.AIEmbeddingService}' is not supported.");

View on GitHub (pinned to c028a0c7dc)

Solutions

Set RagConfig:AIChatService to exactly 'AzureOpenAI' or 'OpenAI' in appsettings.json or user secrets.
If you need another provider, add a new case arm to the switch and register the appropriate chat completion service.
Verify there are no trailing spaces or casing differences in the configured value.
Make the switch case-insensitive with StringComparison to reduce friction.

Example fix

// before — only two providers, case-sensitive
switch (appConfig.RagConfig.AIChatService)
{
    case "AzureOpenAI": /* ... */ break;
    case "OpenAI": /* ... */ break;
    default:
        throw new NotSupportedException($"AI Chat Service type '{appConfig.RagConfig.AIChatService}' is not supported.");
}

// after — case-insensitive with clear valid-values list
switch (appConfig.RagConfig.AIChatService?.ToLowerInvariant())
{
    case "azureopenai": /* ... */ break;
    case "openai": /* ... */ break;
    default:
        throw new NotSupportedException(
            $"AI Chat Service type '{appConfig.RagConfig.AIChatService}' is not supported. Valid values: 'AzureOpenAI', 'OpenAI'.");
}

Defensive patterns

Strategy: validation

Validate before calling

// Validate the value before the switch
var validChatServices = new[] { "AzureOpenAI", "OpenAI" };
if (!validChatServices.Contains(appConfig.RagConfig.AIChatService))
    throw new ArgumentException($"AIChatService must be one of: {string.Join(", ", validChatServices)}. Got: '{appConfig.RagConfig.AIChatService}'");

Type guard

bool IsValidChatService(string? s) => s is "AzureOpenAI" or "OpenAI";

Prevention

Document all valid enum-like string values in configuration comments.
Consider using an actual enum or a Options<T> with validation instead of raw strings.
Make switch matching case-insensitive to reduce friction.

When it happens

Trigger: The RagConfig.AIChatService configuration value is set to a string that is not exactly 'AzureOpenAI' or 'OpenAI' (case-sensitive) — e.g., 'azureopenai', 'Azure', 'Anthropic', or null/empty.

Common situations: Typo or casing error in the configuration file or user secrets; the value is left empty or unset (null); an expected future provider hasn't been added yet; copy-pasting a config from another sample with a different provider naming scheme.

Related errors

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/e8d7becc7cad87cf. Report an issue: GitHub.