In .NET 9 string.contains("X") will delegate to string.contains('X')

StringContains.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Columns;
using BenchmarkDotNet.Configs;
using BenchmarkDotNet.Environments;
using BenchmarkDotNet.Jobs; 
using BenchmarkDotNet.Reports;
using BenchmarkDotNet.Running;

BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

[Config(typeof(Config))]
[HideColumns(Column.Job, Column.RatioSD, Column.AllocRatio)]
[MemoryDiagnoser]
public class StringContains
{
    readonly string _inputString =
        "Permission is hereby granted, free of charge, to any person obtaining " +
        "a copy of the Unicode data files and any associated documentation";

    [Benchmark]
    public bool Contains_string() => _inputString.Contains("X");
    private class Config : ManualConfig
    {
        public Config()
        {
            AddJob(Job.Default.WithId(".NET 8").WithRuntime(CoreRuntime.Core80).AsBaseline());
            AddJob(Job.Default.WithId(".NET 9").WithRuntime(CoreRuntime.Core90));

            SummaryStyle =
                SummaryStyle.Default.WithRatioStyle(RatioStyle.Trend);
        }
    }
}