There is no maximum period.
All Long Bets are about things that matter, directly or indirectly.
Long Bets are not guesses. Each predictor has a theory of how the world will proceed, and that theory is made explicit. At the conclusion of each Prediction or Bet there will be public examination of the original argument(s), to see how they match with reality.
For that, the Prediction will be kept accessible in perpetuity, along with its Discussion and Voting record. The fee is payable on acceptance by The Long Now Foundation of the Prediction for publication.
Registration is free. Your name and vote becomes a permanent part of the record of the Prediction or Bet. Your vote cannot be changed later. Votes made under a false name will be removed from the record and the tally.
Any visitor to the site may view anything on the site, including all Discussions, but you must be a registered user to join a Discussion.
Long Bets is about taking personal responsibility for ideas and opinions. Posting, voting, and predicting under your true name is part of standing up for what you think.
Anyone may challenge a Prediction, and must offer their own argument for why they think they will be proved right, but the challenge does not become a Bet until the original Predictor has accepted the Challenger, and they have agreed upon the stakes. In some cases a Predictor and Challenger will arrive together on the site with a Bet already in mind. Like Predictions, Bets must be approved by the The Long Now Foundation before they go On the Record.
There is no maximum amount. The bet money, treated as a donation to the The Long Now Foundation, must be paid at the time the Bet is made, and is tax-deductible immediately. The entire amount goes into a long-term investment portfolio called the Farsight Fund --- its assets are in "Endowments", a mutual fund managed by Capital Research and Management Company. Half of the growth of that fund is drawn off to The Long Now Foundation, which maintains the Long Bets service; the other half accrues so that the eventual payment to the winner's preferred charity may be significantly larger than the original bet stakes. The original Predictor pays $50 less into the stakes than the Challenger, because of already having paid the original $50 publication fee.
Odds-making is for gamblers, not the game here. A win/lose outcome helps force lucidity in the original terms of the bet and in the eventual judgement about who won. At the resolution of the bet, if both bettors are still alive and both agree on who won, that concludes the matter. Otherwise, The Long Now Foundation will adjudicate who won. The outcome will be announced and discussed publicly - that's the whole point: to see competing predictions through to completion and learn from the result.
The charity designated should be IRS-approved if in the US. Foreign charities also are eligible. The Long Now Foundation cannot legally guarantee that the winnings will go to the winner's preferred charity. It is highly motivated to do so, of course, since how a bet is resolved is in the public eye.
At the conclusion of a bet, the winner's original choice for a charity may have disappeared or been transformed by time or been superseded in the winner's interest. The winner, if still alive, may then choose a different charity. If the original charity has disappeared or changed radically, and the winner is not alive, The Long Now Foundation may pick an alternative charity it deems closest to the winner's original intention.
The Bettor's Agreement helps protect the foundation's longevity - and thereby the Long Bets and long bettors - in an environment of strong financial interests and intellectual conflict, in a nation that outlaws private gambling. Far from boilerplate, the agreement has been carefully researched and refined for its specific use.