> ## Documentation Index
> Fetch the complete documentation index at: https://docs.peec.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# ChatGPT Shopping runs on OpenAI's own product index — live A/B experiments

> Peec's investigation (Sep 2026) — five live A/B experiments test OpenAI's own product index in ChatGPT Shopping; ranking blends BM25, a 400-candidate reranker and vector search.

ChatGPT Shopping is where OpenAI's own search index is most visible in production. Peec's investigation ([full study](https://peec.ai/blog/chatgpt-built-its-own-search-index), Sep 2026) spotted an A/B experiment named "prefer-index-over-serp-v3" in ChatGPT's server-side events in mid-August 2026, affecting 8% of chats at the time — OpenAI testing its own product index against scraped search results on traffic slices from single digits up to 20%.

As of September 2, 2026, at least five separate shopping experiments were running: prefer-index-over-serp-v3, chatgpt-shopping-noamazon, shopping-index-q2qb, shopping-hqi-v2, and shopping-hq-v1. Whether "hqi" stands for "high quality index" is not confirmed; what is confirmed is that both prefer-index-over-serp-v3 and shopping-index-q2qb run on ChatGPT's own index — see [ChatGPT has its own search index](/research/chatgpt-own-search-index-labrador).

The ranking stack behind one experiment ("shopping-reduced-topn-v4b"), visible in the same events:

* **BM25 lexical component** — narrows the field to 10 sources for ranking.
* **rerank400** — reranks a pool of 400 candidates.
* **prod400** — 400 products used as the input pool.
* **ann4096** — approximate nearest neighbor (vector search), run at two dimensions: 12,288 and 4,096.

Multiple ranking signals blended, then A/B tested against real traffic until the mix earns its place in production. The study's advice for anyone selling products: watch how you show up in ChatGPT's shopping results specifically — that is where the index push affects product selection today.

**Source:** [ChatGPT built its own search index](https://peec.ai/blog/chatgpt-built-its-own-search-index), Peec (Tomek Rudzki), Sep 2026.