What changed in AI search this fortnight

Vendor moves

OpenAI had its biggest week since the GPT-5.6 transition in August. GPT-6 Astra arrived September 3 as the new flagship, reaching paid ChatGPT tiers a day later, with computer use, coding, and long-horizon agent work as the headline capabilities. If you simulate ChatGPT for testing, note the mechanics: no temperature or top_p control, tool calling requires the Responses API, and an asynchronous alignment monitor can pause agent runs mid-task for review. On the commercial side, OpenAI pushed ChatGPT Ads to self-service in 52 countries, including Europe, India, and the Middle East and North Africa, and the ad stack now includes audience management above 5 million members, conversion measurement, pacing, and reporting. OpenAI frames advertising as what funds free access. Call it what you want. This is a real ad platform now, past the pilot stage.

Google's week ran on three tracks. On models: Gemini 3.8 Flash launched September 2 and reached AI Mode the same day for Pro and Ultra subscribers, three weeks after the previous swap. On measurement: the Search Console generative AI performance reports and the new AI opt-out control finished a worldwide rollout around August 31, ending a staged release that started with the UK back in July. The reports remain impressions-only, with no click data attached. On legal: a federal judge declined to break up Google's ad tech business on September 2, rejecting a forced sale of its ad exchange and imposing new rules on how the auctions run instead. A joint final judgment is due October 2. The measurement layer that funds most of the open web stays under one roof, with new conduct rules attached to it.

Perplexity's public output this fortnight was a widely shared explanation of its own mechanics: every answer starts with embedding and ranking models choosing sources before anything gets written, a rare first-party account of how a retrieval-based answer engine actually works. The company's changelog page itself returned nothing but a cookie wall to research tools, so treat this fortnight's Perplexity coverage as thinner than usual. One item worth a flag if you run WordPress: a competing plugin developer alleges that Rank Math, installed on roughly 4 million sites, creates an administrator-level application password for its parent company when a free-tier user opens the Help screen. Rank Math has not responded publicly. Nothing is confirmed yet, but if you or a client runs Rank Math, it costs nothing to check.

How LLMs read the web

The RESONEO study is the one to read twice. OpenAI operates its own discovery index for ChatGPT's free instant answers, serving full page titles and a roughly 200-character snippet anchored on the page's H1, static across queries. A shared reading cache stores HTML-to-Markdown conversions of popular pages, refreshed about every 30 minutes, and it disregards both noindex and Cache-Control no-store: once a page is cached, it is available to the model whether the publisher wants that or not. Pages over 4 MB return errors and are effectively invisible. JavaScript never runs. Live page fetches are mostly reserved for paid Thinking mode, where a freshly opened page gets cited 74% of the time, against 7% for cache-only hits.

Here is the part that changes how you report on ChatGPT: free-tier answers pull almost entirely from that internal index, while paid Thinking mode leans on scraped Google results, 75.3% of its retrieval in the data RESONEO collected. Ask the same question on a free account and a paid Thinking-mode account and you may be looking at two different source pools. A single \"does ChatGPT mention us\" check is incomplete without saying which tier and which mode. This connects to a story from the prior fortnight: Google confirmed it now rewrites every search result link through an encoded google.com/goto redirect, aimed squarely at scrapers. Here is the most visible scraping customer there is, using pipelines named after Bright Data and Oxylabs to read those same results. It is one story about who pays to read Google, told from both ends.

One detail worth keeping in your back pocket: URLs cited in ChatGPT answers without a visible snippet were cited more often than snippeted ones, 14.9% against 8.2%. That gap points to some citations coming from the model's training data rather than a live fetch, which is a reason not to read every citation as proof a page was actually retrieved.

On llms.txt: after months of evidence that no answer engine reads the file for citation purposes, the first demonstrated effect of the file is a security one. Researchers examined 8,565 llms.txt and llms-full.txt files across 6,214 active domains and found 237 references to packages and domains nobody had claimed. In one case, documentation referenced a package that did not exist; a researcher registered it, and the first installation callback from a Fortune 500 network arrived in under four minutes. Coding agents treat vendor documentation as trusted input and do not check whether a referenced package or domain actually belongs to the vendor that published it. If you or a client maintains an llms.txt file, the fix is cheap: reference only packages, domains, and commands the organization actually controls, and audit whatever is already published.

On the presentation side, Google's AI Overviews now expand automatically for some queries, based on what the company says its systems judge most useful for a given topic. Retrieval does not appear to change here. What changes is the render: a fully expanded Overview pushes the first organic result well down the page and leaves the citation slots inside the answer as the only prominent thing to click.

Community signal

Aleyda Solis carried the ChatGPT index story to a wider audience (133 likes, 12.6K views) and flagged the Search Console rollout the same week. Perplexity's own thread explaining its embedding-and-ranking mechanics was the fortnight's loudest watchlist item, 512 likes and 119.6K views, and it is worth citing to clients directly as a first-party source. Barry Schwartz's daily coverage tracked the ad tech ruling, AI Mode's continued spread across the results page, and an early, unconfirmed report of degraded Gemini citation behavior that we are holding as a lead only.

The open-terms conversation on X produced one real argument worth knowing. David Quaid called the claim that ChatGPT has its own index a poorly reasoned position pushed by GEO agencies. The RESONEO measurement now argues the other side directly: the index is not a matter of opinion anymore, it is measured. Two numbers circulated without a source behind them and belong nowhere near a client deck: a claim that ChatGPT passed 159 million monthly searches in the EU, and a claim that LinkedIn's AI citation rate fell from 13.8% in February to 4.8% in July. Both are single-post claims with no primary study underneath.

Reddit stayed noisy for a fourth straight fortnight, with most search-leg threads off-topic and both community threads amounting to tool self-promotion. The comment sections did the real work again. On a thread about a free AI visibility checker, the top comment argued that a single 0-100 score should be secondary to the evidence behind it: show the exact questions, engine, locale, date, and response text, separate mention presence from citation quality, and let people rerun the prompts themselves to see what changed. That is a better measurement standard than most paid dashboards offer. A separate thread in r/GEO_optimization celebrated Google's own guide to what you do not need to do for AI visibility, no llms.txt, no chunking, no AI-specific rewriting, as having quietly ended half the GEO sales pitches making the rounds this year.

What it means for your brand

Pull your Search Console AI performance baseline now, while the reports are still new, and confirm the AI opt-out control has not been switched on for any property you manage. That toggle can zero your Google AI visibility with nothing in the interface to explain why, and the reports themselves only show impressions, not clicks, so treat this as a starting line, not a scoreboard.

Check your key pages against what ChatGPT's free tier actually reads: a full title, a snippet anchored on your H1 and the first couple hundred characters of body copy, nothing over 4 MB, nothing that depends on JavaScript to render. This costs editorial time, not budget, and it is the most concrete on-page guidance this newsletter has had to offer in six issues.

Add a tier and mode qualifier to any ChatGPT visibility claim you report internally or to a client. Free and paid Thinking-mode answers draw from different source pools, so \"we show up in ChatGPT\" is not a complete sentence anymore. Say which ChatGPT.

Mark September 2 and September 4 on your measurement calendar. Any citation movement in Google's AI Mode after the 2nd or in ChatGPT after the 4th is more likely the new model than anything you changed on your site. Comparing before and after those dates without the boundary noted will make ordinary model noise look like a content problem.

If you or a client publishes an llms.txt file, audit it this fortnight. Reference only packages, domains, and commands your organization actually controls, and remove or fix anything else. The file still does nothing for citations. It can now do real harm if left careless.

If ChatGPT Ads self-service reaches your markets, 52 countries as of September 3, it costs one look to price out what a paid presence would buy, even if the answer is to stay earned-only. The sponsored-placement question has been on this list for months. It is now something you can check without a sales call.