microsoft/autogen · error · Exception

Missing MISTRAL_API_KEY environment variable.

Error message

Missing MISTRAL_API_KEY environment variable.

What it means

Startup guard in the Mistral token-count sample: it reads MISTRAL_API_KEY and throws a plain Exception if absent, because MistralClient cannot authenticate without it. The throw happens in RunAsync before the MistralClientAgent or any middleware (token counter, message connector) is constructed; it is sample code, not the Mistral/AutoGen library.

Source

Thrown at dotnet/samples/AgentChat/AutoGen.Basic.Sample/Example14_MistralClientAgent_TokenCount.cs:42

            if (reply is IMessage<ChatCompletionResponse> message)
            {
                responses.Add(message.Content);
            }

            return reply;
        }

        public int GetCompletionTokenCount()
        {
            return responses.Sum(r => r.Usage.CompletionTokens);
        }
    }
    #endregion token_counter_middleware

    public static async Task RunAsync()
    {
        #region create_mistral_client_agent
        var apiKey = Environment.GetEnvironmentVariable("MISTRAL_API_KEY") ?? throw new Exception("Missing MISTRAL_API_KEY environment variable.");
        var mistralClient = new MistralClient(apiKey);
        var agent = new MistralClientAgent(
            client: mistralClient,
            name: "assistant",
            model: MistralAIModelID.OPEN_MISTRAL_7B);
        #endregion create_mistral_client_agent

        #region register_middleware
        var tokenCounterMiddleware = new MistralAITokenCounterMiddleware();
        var mistralMessageConnector = new MistralChatMessageConnector();
        var agentWithTokenCounter = agent
            .RegisterMiddleware(tokenCounterMiddleware)
            .RegisterMiddleware(mistralMessageConnector)
            .RegisterPrintMessage();
        #endregion register_middleware

        #region chat_with_agent
        await agentWithTokenCounter.SendAsync("write a long, tedious story");

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Create an API key at console.mistral.ai and export MISTRAL_API_KEY in the launching shell before running the sample.
2. Add MISTRAL_API_KEY to the IDE run profile / CI secret store if you launch or build the samples there.
3. Confirm the variable name matches exactly — the sample reads only MISTRAL_API_KEY.
4. Verify the key has access to OPEN_MISTRAL_7B (the model used by this sample) to avoid a follow-up auth/model error.

Example fix

// before
var apiKey = Environment.GetEnvironmentVariable("MISTRAL_API_KEY") ?? throw new Exception("Missing MISTRAL_API_KEY environment variable.");

// after
var apiKey = Environment.GetEnvironmentVariable("MISTRAL_API_KEY")
    ?? throw new InvalidOperationException("MISTRAL_API_KEY is not set. Create a key at console.mistral.ai and export it before running.");

var apiKey = Environment.GetEnvironmentVariable("MISTRAL_API_KEY");
if (string.IsNullOrWhiteSpace(apiKey))
{
    Console.Error.WriteLine("MISTRAL_API_KEY is not set. Create a key at console.mistral.ai and export it.");
    return;
}

try
{
    await Example14_MistralClientAgent_TokenCount.RunAsync();
}
catch (Exception ex) when (ex.Message.Contains("MISTRAL_API_KEY"))
{
    Console.Error.WriteLine($"Missing Mistral credential: {ex.Message}");
}

When it happens

Trigger: Invoking Example14_MistralClientAgent_TokenCount.RunAsync() when MISTRAL_API_KEY is unset/empty in the process. Distinct from the OpenAI samples: this key comes from console.mistral.ai, not OpenAI.

Common situations: Having only OPENAI_API_KEY set (most AutoGen samples need OpenAI) and running the whole sample project; no Mistral account/key provisioned; key exported under a different variable name (e.g. MISTRAL_API_KEY vs MISTRAL_KEY).

Related errors

• Please set OPENAI_API_KEY environment variable.
• Please set OPENAI_API_KEY environment variable.
• BING_API_KEY environment variable is not set
• Please set OPENAI_API_KEY environment variable.
• Please set OPENAI_API_KEY environment variable.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/6034f2a3bbcf06c4. Report an issue: GitHub.