Taiwan High Speed Rail already posted the calendar: National Day movement runs October 8 through 12, with reservations open since September 10. Double Tenth falls on Saturday, October 10; the government moved Friday the 9th as the compensatory holiday, so the useful travel days are Thursday evening through Monday morning.
That matters because the last long weekend just broke a daily record. THSR carried about 348,000 passengers on Thursday, September 25, the eve of Mid-Autumn, then 315,000 on Friday. Non-reserved cars spilled into reserved and even business coaches. The operator had to remind riders that standing in a dearer car can trigger the fare difference plus a 50 percent penalty.
Do not assume the next holiday will be quieter. Book a reserved seat on the THSR site or T-EX app now if you are leaving Taipei on the 8th or 9th or coming back on the 11th or 12th. Early-bird discounts exist on some off-peak trains if you are still inside the window; peak holiday departures usually are not discounted. Foreign passports work if the number on the booking matches the document you show at the gate.
Non-reserved tickets remain the overflow valve. Use the wait-time lamps on the company site, the app, or LINE TODAY and travel on a green slot if you can. Banqiao and Taoyuan often board faster than Taipei Main when the concourse jams. If you only need Taichung or farther south, a reserved car is worth the extra minutes of booking.
A second holiday follows two weeks later: Retrocession weekend, October 23–27, with extra trains already announced. Anyone planning both trips should treat National Day as the tighter of the two. Mid-Autumn proved the system will pack the aisles before it adds enough cars to feel empty.