An out-of-position 3-bet from the big blind is weighted to value; respond with position and honest ranges.
The reference tier. 4-bet a tight value range, call with hands that flop well, fold the rest without ceremony.
The big blind 3-bets your cutoff steal. The discount made their call cheap — the 3-bet means they chose not to take it.
Assumes a standard 3-bet; 4-bet to ~2.2–2.5x the 3-bet. Deep, favor calls over 4-bets — a 4-bet pot at 500bb+ commits you with range disadvantage.