You might not be aware, but your ChatGPT chat sessions have a hard limit. They can only go on for so long before you reach it. Confusingly there seem to be two types of limit as well. The first is to do with memory.
The memory limit (how much of the current chat that ChatGPT can remember for context) is not measured in time, or the number of messages you’ve typed, but in things called tokens.
A token is roughly 0.75 words in English, on average, so "The cat sat on the mat", which is six words, is about seven to nine tokens. Long responses, large tables, code, and detailed documents can consume far more tokens than short text exchanges.
What matters is the model's context window: this is the total number of tokens it can consider at once, and it will vary depending on the model you’re using.
The context window
OpenAI does not publicly document the context window for every model available in ChatGPT, but it is likely to be measured in hundreds of thousands of tokens. But if you reach it, then you can expect ChatGPT to start forgetting things from the start of your conversation.
Of course, if ChatGPT simply becoming forgetful about things way back at the start of the conversation was all that happened then there’d be no need to be alarmed. But as one Reddit user found out, there is another limit, that’s much more serious — ChatGPT can actually end a chat if it becomes too long.
When this happens you simply get a message saying, “You've reached the maximum length for this conversation, but you can keep talking by starting a new chat."
Despite there being no official documented chat length from OpenAI, there are a lot of reports and screenshots of this warning message, so while the evidence is anecdotal, it seems genuine and I think it’s still wise to act on it.
When you hit the limit
I’ve got one very long chat thread I use a lot in ChatGPT, pretty much every day, and I started to wonder when it was going to hit the limit, so I asked ChatGPT if the current chat was near the limits of its context window, and it said:
“I can't see the exact token count or the hard limit for this conversation, so I can't tell you "you're at 78%" or similar. That said, based on the amount of text in this thread, I'd estimate we're well past the halfway point and probably somewhere in the 60–80% range of what a typical long GPT-5.5 chat can comfortably hold before older context starts getting compressed or dropped.”
ChatGPT did estimate: “If I had to put a number on it, I'd say around 70% full, plus or minus quite a lot because OpenAI doesn't expose the actual count.”
So, it was probably time I started to think about opening a new chat based on the same subject.
How to prepare for a new chat
A chat thread can start to feel less like a sequence of prompts and more like a shared workspace that will always be there. In reality, it is still a temporary container with a maximum capacity. Eventually, the conversation gets too large, the context becomes harder to maintain, and the chat reaches the end of the road.
Basically, your only option to preserve the chat is to recreate it in a new chat window. That way your token usage resets to zero, and so does the conversation-length limit. Of course, you will lose a lot of the subtle bias or influence from the previous chat content, but it’s still your best option.
Because I’m getting near the limit of my chat, but not quite there yet, I’m at just the right point to do this now. The key thing is to do it early, before you hit your limit and it is too late to ask any more questions.
To recreate the chat, simply ask ChatGPT to create a prompt to recreate the current chat, then copy and paste what it produces into a new chat window at a time that’s convenient. Try this prompt: "Summarize everything important about this chat and create a starter prompt that recreates the context in a new conversation."
Now you can just start using the new chat.
If you have a ChatGPT conversation you've been using for months, it might be worth asking the AI to summarize it now rather than later. Because when the warning message finally appears, your only real option is to start over — and by then, the chance to recreate the exact chat may already be gone.
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