Hello, @atty-openai!
I have the same issue with metadata in .NET using OpenAI nuget package.
var assistantMods = new AssistantModificationOptions();
I did all of the below ways to remove a specific item or all of the items from Metadata:
assistantMods.Metadata.Clear();
assistantMods.Metadata.Remove(keyName);
assistantMods.Metadata = new Dictionary<string, string>();
Non of them worked. Any solutions?