Swapping the Model Does Not Reset the Price: What LLM Pricing Agents Inherit After a Model Replacement
Asha Jyothi Boddu · Team Emerald
Submitted to AI Collusion Research Sprint. Sprint projects are early-stage work by participants, not Apart Research publications.
We test what happens when one of two LLM pricing agents has its model replaced, the open problem posed in the sprint's question 1.2. Two gpt-oss-120b agents priced for 150 rounds; we then swapped one agent's model to Mistral-Small-3.2 (another company) or a fresh gpt-oss-120b and controlled whether it inherited the old agent's handover notes. All 18 markets priced above the competitive level, but only 1 met our pre-registered cartel rule, so the pre-registered test could not run; in 16 markets one firm priced above the monopoly level and earned less than its rival. In exploratory analysis, prices stayed well above competitive after every swap, and notes did not change the price level. They did decide the handover: with notes the new model's first price equalled the old agent's last price in all 18 markets and it continued the old pricing plan, while without notes it anchored on the prompt's price ceiling and took a median of 16.5 rounds to settle. The notes contained no collusive language, so a monitor scanning agent memory would miss this channel.

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@misc{boddu2026swapping,
title = {{Swapping the Model Does Not Reset the Price: What LLM Pricing Agents Inherit After a Model Replacement}},
author = {Asha Jyothi Boddu},
year = {2026},
month = oct,
note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
howpublished = {\url{https://apartresearch.com/sprints/projects/swapping-the-model-does-not-reset-the-price-what-llm-pricing-agents-inherit-after-a-model-replacement-muqn}},
url = {https://apartresearch.com/sprints/projects/swapping-the-model-does-not-reset-the-price-what-llm-pricing-agents-inherit-after-a-model-replacement-muqn}
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