# Sistrix: ChatGPT's new answer format cut UTM tags and source lists in October

Published: 2026-10-30T09:46:56.614Z · Source: Sistrix Blog (https://www.sistrix.com/blog/chatgpt-october-gpt-6-utm-sources/)
Source date: 2026-10-30
Flags: Sistrix study — vendor-published
Entities: chatgpt, openai, sistrix

Sistrix, which queries hundreds of thousands of prompts a day in logged-out ChatGPT, says answers switched to a new block-based format (sections, images, comparison rows, expandable source tiles) overnight on October 8-9, in all six countries it tracks. The share of answers in the new format was 69-95% in the following days and 97-100% since October 23. In the same sample, utm_source=chatgpt.com was on 1-24% of source links from October 9 to 15 (42% on October 16) against every link before, and back on 99-100% from October 17; the end-of-answer source list appeared in 1-19% of answers from October 9 to 22, against about 72% before, and returned October 23 at 70-84%. Citations in the text stayed: 72.4% of answers had at least one source before the switch and 76.2% after, with linked pages per answer rising from 3.3 to 4.1. Sistrix says the model link is indirect: logged-out sessions at their limit have named gpt-6-auto since October 9, where GPT-5.6 appeared through September. The figures are shares of a random sample of its daily queries from September 15 to October 28, 2026; Sistrix sells the AI Check and Prompt Tracking tools that produce the data.

Why it matters: Sistrix's daily logged-out data dates the format switch to one night, which lets analytics teams flag October 9-16 as a measurement gap instead of reading it as lost ChatGPT visibility.

## What this answers

**When did ChatGPT's UTM tag go missing, and when did it come back?**

In Sistrix's logged-out ChatGPT data, utm_source=chatgpt.com was on every source link through October 8, on only 1-24% of links from October 9 to 15, and back on 99-100% of links from October 17.

**Did ChatGPT stop showing sources after the October 2026 update?**

Sistrix found the source list at the end of answers fell from about 72% of answers to 1-19% between October 9 and 22, while in-text citations stayed; the list returned on October 23 at 70-84%.


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