Article Title: TSP Update: Changes to TSP Withdrawal Options Q and A (PDF)
Snippet of Article: "...Currently, when you take a withdrawal, the money comes from your traditional and Roth balances on a pro rata basis. For example, if 80% of your account is in your traditional balance and 20% is in Roth, any withdrawal you take will be 80% traditional and 20% Roth. Under the new rules, you can still use this method, but you’ll also have the option to take your withdrawal only from your Roth balance or only from your traditional balance. These options will be available for all types of withdrawals..."
Source: www.tsp.gov