Top-level statements: Program.cs without explicit Main method

Prior to C# 9, every application required a Program class with a static Main method, adding boilerplate even for simple applications and making the hosting model harder to read.

Use top-level statements directly in Program.cs — no namespace, no class, no Main:

// Program.cs
var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddDbContext<AppDbContext>(opt =>
    opt.UseSqlite(builder.Configuration.GetConnectionString("Default")));

var app = builder.Build();

app.UseHttpsRedirection();
app.MapControllers();

app.Run();

For integration tests that need access to Program, add a partial class declaration at the bottom:

// Program.cs last line
public partial class Program { } // allows WebApplicationFactory<Program>

Top-level statements are syntactic sugar. The compiler wraps the code in a generated Program class with a synthetic Main method. This is identical at the IL level to the explicit form.