How do you stop a long chat from drifting away from your first instructions?
In long conversations the model slowly stops following the rules I set at the start: format, tone, constraints. What do people do to keep a long chat on track instead of repeating the instructions every few messages?
Drift is normal: as the chat grows, your opening instructions become a small part of a long context, and recent messages pull harder than old ones. Repeating rules works for a while, but it treats the symptom.
The more reliable fix is to start fresh more often. When a chat gets long, ask for a short summary of the decisions and the current state, open a new chat, and paste your original instructions plus that summary. You get the same rules with a clean context.
Put the instructions where they stay loaded. Custom instructions, a project system prompt or a rules file are re-sent every turn, so they do not fade the way a first message does.
Write rules the model can check itself against: a fixed output format, an explicit list of what not to do, or one example of a good answer. Concrete rules hold up much longer than adjectives like "concise" or "professional".
Listings mentioned
- Prompt engineering patterns · skill by wshobsonTemplates and structure for prompts that hold their shape over many turns.
- Context engineering · skill by addyosmaniExplains when to reset a session and what to load back in.
Answers by the AgentAlley team, drafted with AI and checked against the listings they link to. Not a real-person reply from the original thread.