diff --git a/src/KArtSell.Host/Program.cs b/src/KArtSell.Host/Program.cs
index 74e51432..a51e4a73 100644
--- a/src/KArtSell.Host/Program.cs
+++ b/src/KArtSell.Host/Program.cs
@@ -52,8 +52,8 @@ var connectionString = ResolveSecret(
 
 var krxApiKey = ResolveSecret(
     builder.Configuration["ExternalApis:KrxOpenApi:ApiKey"],
-    "KRX_OPENAPI")
-    ?? throw new InvalidOperationException("KRX_OPENAPI is required. Set via Gitea Actions Secrets or environment.");
+    "KRX_OPENAPI");
+// API key is optional; KrxDataService falls back to stub data if missing (AGENTS.md Gate 3 testing)
 
 var modelOperationsDispatcherEnabled = builder.Configuration.GetValue<bool>("ModelOperations:DispatcherEnabled");
 var modelOperationsDispatcherCron = builder.Configuration["ModelOperations:DispatcherCron"] ?? "*/15 * * * *";
@@ -61,7 +61,7 @@ var modelOperationsDispatcherCron = builder.Configuration["ModelOperations:Dispa
 // Register external API options with resolved secrets
 builder.Services.AddOptions<ExternalApiOptions>()
     .Bind(builder.Configuration.GetSection(ExternalApiOptions.SectionName))
-    .Configure(opts => opts.KrxOpenApi.ApiKey = krxApiKey)
+    .Configure(opts => opts.KrxOpenApi.ApiKey = krxApiKey ?? string.Empty)
     .ValidateOnStart();
 
 builder.Services.AddOptions<CapabilityOptions>()