It depends on the tool. In paid Copilot you are unlikely to hit a limit on memories, while tools like Claude and Mistral do cap them. Custom instructions are limited to about 8,000 characters because they are sent in full with every message. Memories are separate items, and only the relevant ones are pulled in.
More in Prompting Tips
Why can I not see a Memory I just saved?
Sometimes it is a sync delay and the list has not caught up yet, so close it and open it again. Sometimes it is a genuine glitch and the memory was never saved, so create it again. To test it, save a second, different memory and see whether that one appears.
Does Copilot remember my Previous chats?
Only if you set it up. You can turn on chat history in Personalisation, but it rarely pulls anything useful out of old chats, so do not rely on it. What reliably carries over is what you save yourself as a memory or in custom instructions. If you use none of these, each chat starts fresh.
Can I share my Custom Instructions with colleagues?
No, custom instructions stay with you and cannot be shared. What you can share is an agent, and only within your own organisation. When someone uses your agent, both sets of instructions apply: their own custom instructions and the instructions built into the agent.