Sometimes a chatbot acts like it’s never heard of something you know is real. Maybe it’s last week’s news. Maybe it’s a detail you mentioned twenty minutes ago in the same chat. Those feel like the same problem.
They’re actually two different limits, and knowing which one you hit tells you how to fix it.
Context Window
The context window is how much text the AI can look at in one conversation: your messages, its replies, and any files you paste in. It’s measured in tokens (chunks of words). Today’s top models from OpenAI and Anthropic handle about a million tokens. OpenAI says a token is about three-quarters of a word in English, so that’s roughly 750,000 words, which is a stack of long novels (ish).
That sounds like plenty, and for most chats it is. But when a conversation runs long enough, the oldest material falls out or gets squished into a summary, and details start slipping. Bigger isn’t automatically better, either. Models tend to pay less attention to stuff buried in the middle of a really long conversation. That slow fade has a name of its own, Context Drift.
Knowledge Cutoff
The knowledge cutoff is the date the model’s training data stops. Anything that happened after that, the model never learned about, unless it searches the web or you paste it in. Ask about something after the cutoff and the model might say it doesn’t know. Or, worse, it might guess, which is how you get a confident answer about an event it never saw.
OpenAI lists April 30, 2026 as the cutoff for its GPT-6 Astra model. Anthropic lists June 2026 as the reliable knowledge cutoff for its current Claude models. And models usually come out months after their cutoff, so even a brand-new one is a little behind on day one.
The tell
Neither one is the AI being dumb. Ask whether it could have seen the thing at all.
If it happened after the cutoff, the model never learned it. The fix is turning on web search or pasting in the info yourself.
If you told it earlier in the same chat and it forgot, you’ve likely run past the context window. The fix is starting a fresh chat with a short recap of what matters.
One is about the calendar. The other is about how much you’ve said. Most of the time, honestly, it’s the second one, cause most of us don’t start new chats nearly as often as we should.