Your custom instructions are truncated from longer sessions

Custom instructions do not appear to the model after a while. They are truncated out to save tokens. Platform instructions remain visible to the model no matter the length. To fix this problem, create a skill with your custom instructions in the SKILL.md and occasionally remind the assistant to refresh the skill registry and review all required skills before responding. If the skill contains a strong hook, like “always read before responding to the user”, it will read your instructions that were removed without notifying you. You must remind the assistant to refresh the skill registry, because the skill registry will also get truncated in longer sessions and the assistant will not remember that they are even available.