From OPM
Agency Automatic (1%) Contributions. When you become eligible, your agency automatically deposits into your TSP account an amount equal to 1% of your basic pay each pay period, even if you do not contribute your own money. After 3 years of Federal civilian service (or 2 years in some cases), you are vested in these contributions and their earnings.
Agency Matching Contributions. When you become eligible, your agency will match the first 3% of basic pay you contribute each pay period dollar for dollar. Each dollar of the next 2% of basic pay will be matched 50 cents on the dollar. You are immediately vested in the matching contributions.