Why does one AI company run several different crawlers?

Because they do different jobs. A training crawler gathers content to bake into the model; a search/indexing crawler builds the live index the model retrieves from at answer time; an inference crawler fetches one specific page because a user asked about it. Each is a separate user-agent so you can allow or block them independently.

If I block GPTBot and ClaudeBot, is my content kept out of AI models?

Not entirely. Common Crawl's CCBot collects a public web archive that's used as a training input by many models, so your content can still reach those models through that back-door even if you block the labs' own training bots. To cut that pipeline you have to block CCBot specifically.

Which crawlers should a brand that wants AI visibility allow?

At minimum the search/indexing and inference bots (OAI-SearchBot, Claude-SearchBot, PerplexityBot, ChatGPT-User, Claude-User). These drive citations and the 'summarize this link' feature. Most brands that want to be discovered also allow the training bots, since being learned by the models means they 'know' you.

The AI crawler lifecycle: train, index, and answer

When people picture an "AI crawler," they imagine one bot hoovering up the web. The reality is more useful to know: a single lab usually runs several bots, each doing a different job. Sort them by job and a lot of confusing robots.txt decisions become obvious.

There are three jobs.

1. Train: baking content into the model

Training crawlers gather content that may be used to train future models. Once something is in the training corpus it's effectively permanent and uncompensated, which is why publishers who monetize content most want to block these.

Who: GPTBot (OpenAI), ClaudeBot (Anthropic), Google-Extended (Gemini training), Applebot-Extended.
Behaviour: broad and periodic. They crawl widely, not in response to any single user.
What blocking does: the next generation of models learns less about you.

2. Index: building the live search index

Search/indexing crawlers build a searchable index the AI queries at conversation time (retrieval-augmented generation). Your content gets retrieved and cited live, but isn't used to train the model.

Who: OAI-SearchBot (OpenAI), Claude-SearchBot (Anthropic), PerplexityBot.
What blocking does: you disappear from AI search answers. Usually the last thing a brand wants.

3. Answer: fetching a page on demand

Inference (or user-triggered) fetchers grab one specific page in real time because a user asked, for example, when someone pastes your URL into a chat and says "summarise this."

Who: ChatGPT-User (OpenAI), Claude-User (Anthropic).
What blocking does: breaks the "summarise this link" experience for your own visitors.

Anthropic's three bots map cleanly onto this. ClaudeBot = train, Claude-SearchBot = index, Claude-User = answer, and OpenAI mirrors it with GPTBot / OAI-SearchBot / ChatGPT-User.

The odd one out: Common Crawl

CCBot doesn't fit any of the three boxes. Common Crawl is a non-profit that crawls the web into a giant public archive: it trains no models itself. The catch: that archive is one of the most widely used inputs for training models across many labs.

Blocking GPTBot and ClaudeBot does not stop your content reaching those same labs through the Common Crawl dataset. To close that back-door you have to block CCBot separately.

So what should you allow?

It depends on your goal, and the decision is per-bot, not a single "AI: on/off" switch:

Want maximum AI visibility? Allow the index and answer bots without question. They're what get you cited and make link-sharing work. Most brands allow training bots too, because being learned by the models means they recognise your brand later.
Protecting proprietary or monetised content? Block the training bots (and CCBot), but think hard before blocking index/answer bots, that's where live citations come from.

Two caveats worth remembering. First, this is all enforced by user-agent, so a site can be visible to one lab and invisible to another purely as a robots.txt artifact (see Should you let AI crawlers index your site?). Second, allowing a bot in robots.txt isn't enough if your CDN blocks it at the edge first (your CDN might be doing exactly that).

Knowing which bot does what is the difference between a deliberate AI strategy and accidentally locking the door on the engines you most want to reach, which is exactly the kind of gap Buffy Intel is built to surface.