Inherited Collusion: Replacing an Overcharging AI Pricing Agent Doesn't Fix It, but One Past Example of a Cheaper Price Earning More Can

If an AI pricing agent is caught overcharging, the obvious remedy is to replace it. We test whether that restores competition. In a simulated two-firm market, two gpt-4.1-mini agents first settle on a high shared price; one is then replaced by a fresh agent that is never told to collude and inherits its firm's price history, while the other firm keeps its price and cannot punish undercutting. Across 20 histories and three newcomer models, the newcomer kept most of the overcharge above its best response to the incumbent's price: gpt-4.1-mini 73%, Qwen3-14B 97%, Claude Haiku 5.5 89%. A newcomer with no history kept the price high too, copying its competitor, so the record is not what sustains the price. Pre-registered levers mostly failed: relabelling the history as a predecessor's, messages from "management", and instructions to compete barely moved prices. What worked was one row in the newcomer's own history showing a lower price that earned more, whether real or inserted: it removed the overcharge for gpt-4.1-mini, halved it for Qwen3-14B and cut it by a sixth to a quarter for Haiku. A sham round and a zero-profit row did nothing; the competitor's low price did far less. For gpt-4.1-mini the change held against a live competitor that never retaliated, lasted 80 rounds and survived deleting the row. At a fixed price, the sales and profit a row reported decided whether gpt-4.1-mini adopted it. A high-price row showing high profit raised prices, so inherited records are an attack surface.