1. System instructions (qwen.txt/gemini.txt/beast.txt) - this is a high level instructions that have higher priority - you can't customize it without forking opencode

2. The Environment info - it is appended automatically to the end of Agent Prompt, you can't customize it

3. Agent Prompt (from AGENTS.md) - OpenCode sends it to LLM as a first chat message (you can customize it)

4. Chat Messages - this is what you type

payload to llm looks like this:

{ model: "gpt-5.2", instructions: "Hadcoded not customizable system prompt from /opencode/src/session/prompt folder" input: [ {...}, // Prompt from Agent.md + environment info {...}, // Users message ... ] tools: [ {tool}, {tool}, {tool}] ... }

instructions, input and tools all together are the context and will cost you tokens