Does switching AI models change what it says about my brand?

Switching models can change what an AI says about your brand. Two separate mechanisms cause it.

The first is the knowledge cutoff. A model only knows what was in its training data up to a fixed date. Anything you announced after that date does not exist for it unless it searches the web. OpenAI's model documentation (verified August 2026) lists a February 16, 2026 cutoff for the GPT-5.6 models (Sol, Terra and Luna). The non-reasoning Instant path, the chat-latest alias, carries an August 31, 2025 cutoff. That is about five and a half months of brand news one path knows and the other does not.

The second is retrieval. When a model searches, it can find your current pages. When it does not, it answers from memory. ChatGPT decides per query whether to search, and it rewrites your question into its own search queries, according to OpenAI's help page on ChatGPT search. So the same question can get a searched answer once and a memory answer the next time.

Put together: a different model can mean a different cutoff, a different search behavior, or both. Your brand facts can shift without anything on your site changing.

Most users never pick a model on purpose. The app picks for them, and that choice varies by plan and over time. This is model routing, and it is the main reason two people get different answers to the same question.

As of a September 2026 snapshot (mostly secondary reports, not vendor confirmation):

• ChatGPT: Free and Go users are reported to get gpt-5.6-luna, Plus users gpt-5.6-sol, and Pro and Business tiers a GPT-6 Pro model. Inside a session, routing between the reasoning family and the Instant path changes the cutoff.
• Claude: Sonnet 5 is reported as the default for Free and Pro, with Opus 5 and other models selectable. Web search is a user toggle.
• Perplexity: Free users get "Best", an auto-router. Paid users can choose from a menu of models from several vendors. See whether Perplexity uses its own model for more.
• Google: the Gemini app added 3.6 Flash to its model menu in July 2026. AI Mode and AI Overviews run on their own Gemini models, and Google says the two "may use different models and techniques."

These defaults move. Treat every line above as a dated observation, not a fixed fact.

The cutoff mechanism is documented by the vendors. The routing between models is documented for ChatGPT and visible in the other apps' menus. What nobody has published is a measurement of how much brand answers actually differ between models for commercial brands.

That gap matters. You can predict that a model with an older cutoff will miss a rebrand or a price change from late 2025. You cannot predict its exact wording, and no outside tool can see which model answered a given user or whether search ran, unless citations appear.

Two more limits apply:

• Memory and custom instructions. OpenAI says ChatGPT may use saved memories when rewriting a search query. Logged-in tests are not reproducible across users.
• API versus app. The Perplexity API, for example, makes web search opt-in on its Agent API. An API test with search off can describe a model no consumer actually meets.

For the full mechanics of searched versus memory answers, read search on vs search off.

You can't change a model's cutoff or its training data this quarter. You can't choose which model a buyer's app routes them to. Nobody outside the vendor controls those.

You do control whether a searching model can reach your current facts. That means:

1. Your key facts (prices, product names, a one-line description) sit in the page HTML before JavaScript runs. Vercel found ChatGPT and Claude crawlers fetch JavaScript files but don't execute them.
2. Your robots.txt allows the search bots, for example OAI-SearchBot, PerplexityBot and Claude-SearchBot, and your firewall does not return 403 to them.
3. Your pages state each fact the same way everywhere, so the engine has one sentence to quote.

None of this guarantees a citation. It removes the blocks between a searching model and your facts. For facts stuck in an old cutoff, see correcting outdated facts past a knowledge cutoff.

A useful test matches your buyers' setup, not yours.

1. Pick the surfaces. Ask sales or check referral data for which apps buyers mention. Note the plan tier if you can, since tier changes the model.
2. Write real buyer questions. Use the questions a buyer would type, such as "best invoicing tool for a five-person agency."
3. Control the session. Test logged out or with memory off where possible.
4. Record four things per answer: the date, the app and plan, the model if shown, and whether citations appeared. Citations tell you search ran.
5. Compare against your facts. Flag what is wrong, missing or outdated, and whether the error lines up with a cutoff date.
6. Retest after changes. When an app announces a new default, rerun the same questions. See what a new model release changes.

The free checker on this site gives a dated snapshot for up to three buyer questions. It is a starting point, not continuous tracking. For ChatGPT errors specifically, fixing ChatGPT errors explains which fixes apply to memory answers and which to searched ones.