The last bitcoin is expected in the year
MMCXL, the year 2140
More than a century from now, by current estimates.
The year
Nobody alive today is likely to see 2140. Everyone alive today helps decide what it inherits.
Bitcoin pays out new coins with every block, and the amount halves every 210,000 blocks. At the expected pace of about one block every ten minutes, the final, smallest reward is estimated to arrive around 2140. After that, the network runs on fees alone.
The date is an estimate, not an appointment — blocks arrive a little faster or slower than planned. MMCXL treats it the way a monument treats a date: as a fixed point on the horizon to measure our choices against.
The name
Roman numerals add symbols from largest to smallest, except when a smaller one stands in front of a larger one — then it's subtracted. XL is fifty less ten: forty. They have been carved into stone for more than two thousand years, which makes them a fitting way to write a date meant to be remembered.
For things meant to last
Make it repairable
What strangers can fix will outlive what only its makers understand.
Write it plainly
Explain the reasons, not only the rules. The future won't have your context.
Prefer open formats
Plain text and open standards stay readable long after products disappear.
Plant what you won't harvest
Some of the best work pays off only after the people who did it are gone.
Leave room
Decide less. Give those who come later space to choose for themselves.
The time wall
Every year from now until 2140, one stone at a time.
Future halving years are estimates, assuming about four years per 210,000 blocks after the April 2024 halving.
Letters to MMCXL
Write to someone who will be alive when the last bitcoin is expected to be mined. Tell them what you hoped for, what you worried about, or what an ordinary day looked like.