in src/dotnet/AzureAI.Proxy/OpenAIHandlers/Tokens.cs [9:18]
public static int GetTokensFromString(string str, string modelName)
{
if (modelName.Contains("gpt-35"))
modelName = modelName.Replace("35", "3.5");
var encodingManager = TikToken.EncodingForModel(modelName);
var encoding = encodingManager.Encode(str);
int nrTokens = encoding.Count();
return nrTokens;
}