microsoft/semantic-kernel · error · InvalidOperationException

OpenAI client not found.

Error message

OpenAI client not found.

What it means

When an AgentDefinition has no ModelConnection, GetOpenAIClient falls back to resolving an OpenAIClient from the kernel's service provider. If none is registered (FirstOrDefault returns null), it throws because no client exists to make calls.

Source

Thrown at dotnet/src/Agents/OpenAI/Extensions/AgentDefinitionExtensions.cs:163

            {
                var endpoint = connection.TryGetEndpoint();
                Verify.NotNull(endpoint, "Endpoint must be specified when using Azure OpenAI.");

                if (connection.ExtensionData.TryGetValue(ApiKey, out var apiKey) && apiKey is not null)
                {
                    return OpenAIAssistantAgent.CreateAzureOpenAIClient(connection.GetApiKeyCredential(), endpoint, httpClient);
                }

                var tokenCredential = kernel.Services.GetRequiredService<TokenCredential>();
                return OpenAIAssistantAgent.CreateAzureOpenAIClient(tokenCredential, endpoint, httpClient);
            }

            throw new InvalidOperationException($"Invalid OpenAI client type '{connection.Type}' was specified.");
        }

        // Use the client registered on the kernel
        var client = kernel.GetAllServices<OpenAIClient>().FirstOrDefault();
        return (OpenAIClient?)client ?? throw new InvalidOperationException("OpenAI client not found.");
    }

    #region private
    private const string Temperature = "temperature";
    private const string TopP = "top_p";

    private static float? GetTemperature(this AgentDefinition agentDefinition)
    {
        Verify.NotNull(agentDefinition);

        if (agentDefinition?.Model?.Options?.TryGetValue(Temperature, out var temperature) ?? false)
        {
            return (float?)temperature;
        }
        return null;
    }

    private static float? GetTopP(this AgentDefinition agentDefinition)

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Register a client before invoking: kernel.AddOpenAIClient(apiKey) or kernel.AddAzureOpenAIClient(endpoint, credential).
2. Alternatively, supply a ModelConnection in the agent definition so the client is built inline.
3. Verify the service is registered in the same Kernel instance passed to the agent.
4. Use kernel.GetAllServices<OpenAIClient>() in a startup check to fail fast with a clearer message.

Example fix

// before
var agent = await OpenAIAssistantAgent.CreateFromDefinitionAsync(kernel, "my-agent");
await foreach (var m in agent.InvokeAsync(thread)) { }
// after
kernel.AddOpenAIClient(apiKey); // or AddAzureOpenAIClient
var agent = await OpenAIAssistantAgent.CreateFromDefinitionAsync(kernel, "my-agent");
await foreach (var m in agent.InvokeAsync(thread)) { }

if (agentDefinition?.Model?.Connection is null &&
    !kernel.GetAllServices<OpenAIClient>().Any())
    throw new InvalidOperationException("No OpenAIClient registered. Call kernel.AddOpenAIClient(...) or add a ModelConnection.");

static bool HasOpenAIClient(Kernel kernel) => kernel.GetAllServices<OpenAIClient>().Any();

try { var client = agentDefinition.GetOpenAIClient(kernel); }
catch (InvalidOperationException ex) when (ex.Message.Contains("OpenAI client not found")) {
    kernel.AddOpenAIClient(Environment.GetEnvironmentVariable("OPENAI_API_KEY")!);
}

When it happens

Trigger: Invoking an agent whose definition lacks a connection block while the Kernel has no OpenAIClient/AzureOpenAIClient service registered via AddOpenAIClient/AddAzureOpenAIClient.

Common situations: Forgot to register the OpenAI client in the DI container; registered it under a different interface or as a non-OpenAIClient type; DI scope/lifetime mismatch so the service is unavailable where the agent runs.

Related errors

• OPENAI_API_KEY is not set.
• AZURE_FOUNDRY_PROJECT_ENDPOINT is not set.
• AZURE_OPENAI_ENDPOINT is not set.
• AZURE_OPENAI_ENDPOINT is not set.
• OPENAI_API_KEY is not set.

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/d26e898c132eac07. Report an issue: GitHub.