SemanticKernel Azure AI Foundry Inference: Azure.RequestFailedException: Unauthorized

Using Microsoft.SemanticKernel library, I have up until today been able to connect and use deployed models (gpt-4.1, text-embedding-ada-002) in Azure AI Foundry with Microsoft.SemanticKernel.Connectors.AzureAIInference.

Now I get a RequestFailedException with the following 401 error.

Azure.RequestFailedException: Unauthorized. Access token is missing, invalid, audience is incorrect (https://ai.azure.com), or have expired.

Status: 401 (Unauthorized)
Content:
{ "statusCode": 401, "message": "Unauthorized. Access token is missing, invalid, audience is incorrect (https://ai.azure.com), or have expired." }
Headers:
apim-request-id: REDACTED
Strict-Transport-Security: REDACTED
X-Content-Type-Options: REDACTED
Date: Tue, 09 Sep 2025 16:20:08 GMT
Content-Length: 146
Content-Type: application/json

I have not changed my code, and not changed the environmental variables for endpoint or apikey.

I tried making a small console application, and that fails as well with the same exception:

var modelId = "gpt-4.1";
var endpoint = "<my-azure-foundry-project-uri>";
var apiKey = "<my-apikey>";

var services = new ServiceCollection();
services.AddAzureAIInferenceChatCompletion(modelId, apiKey, new Uri(endpoint));

var chatCompletionService = services.BuildServiceProvider().GetRequiredService<IChatCompletionService>();

var history = new ChatHistory();
history.AddUserMessage("What's the weather");

var result = await chatCompletionService.GetChatMessageContentAsync(history);
Console.WriteLine(result);

Any insights would be appreciated.