From January 1, 2026, the GST portal permanently blocks filing of returns older than three years from their due date. This is not a soft warning or a deferral. Once a period crosses the three-year line, it is blocked forever. Any unreported tax or unclaimed ITC for that period is gone — while exposure to demand and penalty under Section 73 or 74 of the CGST Act remains. Which Returns Are Affected? The three-year filing bar applies to GSTR-1, GSTR-3B, GSTR-4 (composition schem