{
 "version": 1,
 "license": "CC BY 4.0",
 "start_usd": 100000.0,
 "asof": "2026-10-20",
 "what": "what virtual $100,000 would be worth today if it had followed the Council's portfolio (the yardstick account) from the start session, and if it had bought the S&P 500 and held; the start is the close before that session (the first session: the league's $100,000), so the start session is counted; the league's own costs are inside; no new AI calls",
 "source": "daily league arena.json: books._council.history, books._spy.history (api/v1/arena-accounts.csv has the same values)",
 "rows": [
  {
   "start": "2026-10-19",
   "council_value_usd": 100032.71,
   "council_return_pct": 0.03,
   "sp500_value_usd": 100087.41,
   "sp500_return_pct": 0.09,
   "council_minus_sp500_pp": -0.05
  },
  {
   "start": "2026-10-20",
   "council_value_usd": 100214.94,
   "council_return_pct": 0.21,
   "sp500_value_usd": 100335.3,
   "sp500_return_pct": 0.34,
   "council_minus_sp500_pp": -0.12
  }
 ]
}