It has most certainly already been extracted and published elsewhere, but I don't think it's been posted here yet, so here is the GPT-5.2 Instant system prompt, android app version (EU), extracted today 19-01-2026. Pretty long (42k+ characters)..

https://github.com/EmphyrioHazzl/LLM-System-Pormpts/blob/main/GPT--5.2%20Instant%2019-01-25%20Android%20System%20Prompt.txt

There are a few minor formatting mistakes left (missing backticks, the tool definition sections have clear blocks with line breaks, etc..) but too lazy to fix it.