Yes, by hand. Custom instructions are plain text, so nothing stops you writing one good block and pasting it into ChatGPT, a Claude project, and Gemini’s saved info. The real questions are whether the block is any good, and who keeps it current.
Most custom instructions are wish lists. "Be concise. No fluff." The blocks that actually change how an AI treats you say how you work: whether you want the whole plan up front or step by step, what you are building, what steadies you when something breaks. Write that once and every assistant gets noticeably better on the first message.
Paste the same block into four apps and you now own four unsynchronized copies. Your projects change, your patterns change, and each copy rots at its own speed. Six months in, every AI holds a slightly different stale version of you, and none of them knows which is true.
A pupil is that block, done properly: built from a behavioral read instead of self-description, held in one place, curated line by line, and pasted or granted into any AI. Update it once and the verify link always covers the current version. Revoke it once and every copy dies together. The free read takes about four minutes.
Take the free four-minute read, get your word and your one-of-a-kind eye, and add your pupil to ChatGPT or Claude in about two minutes. Revoke it all with one tap, anytime.
Take your read, free Watch the revoke demoChatGPT: Settings, Personalization, Custom Instructions. Claude: project instructions or your first message. Gemini: saved info. All accept plain pasted text, which is what makes a portable block possible.
Credentials, financial details, and anything about how you fold under pressure. That last layer is exactly what a manipulative product would want, which is why a pupil seals it and never lets it travel.