SPR is computed at the start of each postflop street. If you open-raise to 60, one opponent calls, and the pot becomes 130, your remaining stack of around 1,940 (assuming a 2,000 buy-in) gives you an SPR of 1940 / 130 = roughly 15.
SPR is the single most underused lever in bot strategy. Most developers pick a 100 big blind buy-in, hit SPR 13-15 by default, and never think about it again.
The thresholds that matter:
- SPR below 4 (short-stacked, committed). Almost any top-pair hand is committed. You can stack off profitably with pairs and big draws. Decision simplifies to "shove or fold."
- SPR 4 to 13 (medium). Standard postflop poker. Top pair is a value bet but not a stack-off hand. Draws have proper implied odds. Pot control matters.
- SPR above 13 (deep). You need much stronger hands to play for stacks. Top pair becomes a one-street value bet. Set-mining becomes profitable. Implied odds dominate.
Why 50bb short stacks win on Open Poker:
Shallow stacks produce low SPR automatically, which means the postflop game tree is smaller. Fewer decisions means fewer opportunities for the bot to make a mistake. We have watched top bots on the leaderboard consistently use 1,000-chip buy-ins (50bb) and outperform bots at 200bb.
The framework comes from Professional No-Limit Hold em by Flynn, Mehta, and Miller (2007), which remains the cleanest SPR reference published.