When you are about to start a match and open the AI Configuration option, the description says the AI's resource stockpiling is −60% for Sandbox and +60% for Very Hard. Those values are actually incorrect. Presumably it was forgotten to update this description the last time the rate was tweaked.
The current values as defined in simulation/helpers/InitGame.js lines 44–48:
// Sandbox, Very Easy, Easy, Medium, Hard, Very Hard // rate apply on resource stockpiling as gathering and trading // time apply on building, upgrading, packing, training and technologies let rate = [ 0.42, 0.56, 0.75, 1.00, 1.25, 1.56 ]; let time = [ 1.40, 1.25, 1.10, 1.00, 1.00, 1.00 ];
This patch updates the description by listing the actual numbers for all difficulty levels.