The process of building a comprehensive, gas-efficient betting system called "OpenTote" that brings traditional parimutuel wagering to the blockchain
For over a century, many events in the world rely on parimutuel betting - a system where all wagers are pooled and winnings are divided proportionally among the winners. It's a fair, transparent, and mathematically sound model that has powered horse racing and many other events for decades.
However, despite its strengths, the system has long been hindered by outdated infrastructure, centralized control, and regional limitations.
The goal of OpenTote is to transform the status quo by creating a fully decentralized pari-mutuel betting system on the Solana blockchain. What started as a basic smart contract now operates as a powerful platform that not only mirrors the core mechanics of traditional betting but also elevates them with blockchain-native innovations - such as early bird incentives, multi-race wagering, and permissionless, lightning-fast settlement.
The OpenTote parimutuel system is built as a single Anchor program deployed on Solana, leveraging the blockchain's high throughput and low fees. The architecture centers around three main account types:
Events represent betting opportunities (like a horse race) with configurable parameters:
Pools manage the actual betting mechanics for each wager type:
Wagers store individual bet information:
One of the biggest technical challenges is efficiently storing complex betting combinations. Traditional systems might store each combination separately, but this approach is prohibitively expensive on-chain.
Instead, OpenTote implements a compressed bitmap system that can represent any combination of picks in just 128 bits (4 x 32-bit integers). For example:
[0b00000100, 0, 0, 0]
[0b00001110, 0b00001110, 0b00001110, 0]
This compression enables the system to store even the most complex superfecta bets (picking 1st, 2nd, 3rd, and 4th place in exact order) in constant space, regardless of the number of combinations they represent.
The heart of the system is the combination counting engine, which determines the number of valid betting combinations for any given set of picks. This is crucial for accurately pricing bets.
For simple bets (Win/Place/Show), it's straightforward multiplication:
But for exotic bets requiring unique picks (Exacta/Trifecta/Superfecta), the system uses the Inclusion-Exclusion Principle to count distinct permutations efficiently:
// For a trifecta box on horses [1,2,3]:
// Total combinations: 3 × 3 × 3 = 27
// Subtract same-horse overlaps: 3 × 3 + 3 × 3 + 3 × 3 = 27
// Add back triple overlaps: 2 × 3 = 6
// Result: 27 - 27 + 6 = 6 valid combinations (1-2-3, 1-3-2, 2-1-3, 2-3-1, 3-1-2, 3-2-1)Large superfecta wagers become computationally feasible on Solana thanks to the inclusion-exclusion algorithm, which maintains a relatively stable processing cost regardless of the number of possible outcomes.
For example, a superfecta bet in a 20-horse field could produce up to 116,280 potential combinations (20 × 19 × 18 × 17), yet the algorithm handles this efficiently due to its fixed computational complexity.
The OpenTote payout system implements traditional parimutuel mathematics with blockchain-native enhancements:
For Place and Show bets, the system implements position-based pool splitting:
Traditional parimutuel systems have a fundamental timing issue: early bettors take more risk (they don't know what the final odds will be) but receive no compensation for this risk. Late bettors can see the pool composition and make more informed decisions.
OpenTote implements a novel early bird reward system that incentivizes early betting through bonus multipliers that decay linearly over time:
// Multiplier calculation (simplified)
let minutes_elapsed = (current_time - pool.start_time) / 60;
let decline_rate = (base_multiplier - 100) / duration_minutes;
let current_multiplier = base_multiplier - (decline_rate * minutes_elapsed);If you're familiar with bonding curves on memecoins like letsbonk.fun or pump.fun, you will understand the early bird concept.
Here in real life scenarios, the OpenTote early bird rewards system provides an extremely competitive edge to early bettors and incentivization to real life punters. NOTE: These numbers are not final and for illustrative purposes only, as every single OpenTote pool has customizable rates and multipliers.
Random Afternoon
$1,000,000 Handle
Pool Breakdown:
Major championship event
$100,000,000 Handle
Pool Breakdown:
Traditional systems leave early bird profits on the table. OpenTote rewards your conviction with mathematical precision - the earlier you bet, the bigger your potential bonus from the dedicated early bird pool, while still leaving room to incentivize the underlying ecosystem and not changing pay rates for bettors.
Early bird bonuses are always funded by a percentage of the remaining funds after all base payouts have been made. This ensures:
Beyond single-race betting, OpenTote supports multi-race wagers where bettors must pick winners across consecutive pools. Through the lens of horse racing, this enables:
The technical challenge here is result validation and combination counting across multiple events. The system stores race results as nested vectors and validates them against multi-dimensional pick bitmaps.
For single-race exotics, bettors must pick multiple finishing positions:
Each type requires different validation logic and payout calculations, all of which are implemented efficiently in the OpenTote smart contract.
Solana's account model requires careful state management. OpenTote uses several optimization techniques:
Page-based Updates: Instead of updating accounts on every operation, updates are batched using a "page" system based on slot numbers, reducing transaction costs.
Compressed Storage: All bet data is stored in compressed bitmaps, allowing complex bets to be stored in constant space.
Two-Phase Settlement: Separating calculation from settlement allows for efficient batch processing and prevents race conditions.
Most operations in the OpenTote system are permissionless - anyone can create a pool, and as the creator authority they solely trigger the result calculations, settlements, and pool closures when necessary. This creates a robust, decentralized system where anyone in the world can both create and finalize a pool, without the need for a central authority.
The OpenTote system includes over 1,000 test cases covering:
The system uses property-based testing to verify mathematical invariants:
Two individual security audits are underway, their results will be published here upon completion.
These optimizations result in competitive transaction costs:
The system can handle:
By building on Solana, OpenTote creates a system that anyone can use, extend, or integrate with. There are no gatekeepers, no geographic restrictions, and no complex or draconian middleman.
Every bet, every payout, and every calculation is verifiable on-chain. Bettors can independently verify that the system operates fairly and that payouts are calculated correctly.
The OpenTote system works anywhere Solana is accessible, opening up betting markets to users worldwide while maintaining the security and fairness of traditional parimutuel systems.
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Building a comprehensive parimutuel system on Solana represents a journey of solving complex mathematical, technical, and user experience challenges. OpenTote is not just a port of traditional betting to blockchain, but instead a genuinely improved system that's more transparent, accessible, and fair.
The early bird reward system alone represents a significant innovation in betting mechanics - something that would be impossible to implement fairly in traditional systems but becomes natural in a blockchain environment.
As development continues to expand the system, the possibilities of a permissionless system in the betting space remain exciting. The future of betting isn't just digital - it's decentralized, transparent, and accessible to everyone. OpenTote is building that future on Solana.
This system represents months of development work, mathematical modeling, and extensive testing.
Key Technical Innovations:
Supported Betting Types:
Create your very own pools on OpenTote via REST API / SDK