[FEATURE]: System prompt mode switcher (Default/Light)

Feature hasn't been suggested before.

I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Problem

The current system prompts are heavy and optimized for frontier models.
This causes issues with:

Smaller local models hitting context limits
Token waste for simple tasks
Users who want minimal prompting for specific workflows
Outdated instructions that don't match current model capabilities (some prompts unchanged for 7+ months)
Conflicts between default prompts and user's AGENTS.md instructions
Overspecification that degrades reasoning in high-capability models default system prompt materiallly freaks out / degrades reasoning of every high reasoning model #10927

Proposal

Add a system prompt mode setting with initial options:

Default: current per-model prompts (anthropic.txt, gemini.txt, etc.) — no changes
Light: minimal prompt with only essential info: tools, basic safety rules, environment

The current proposal covers several things at once:

Non-breaking: Default behavior unchanged
Extensible: Opens path for future custom mode where users provide their own prompt
Addresses multiple issues without requiring prompt rewrites

Configuration

Via settings menu (Ctrl+P → Settings)
Via opencode.json:

{
   "prompt": {
     "mode": "light"
   }
 }

Related issues

I'm running a local model with 32k context and it works really well for my use case; however, OpenCode's system prompt is consuming ~10% of that context window. If we could get a configuration option to replace the default system prompt with the agent/model prompt we specify, that would solve this and all of the other related issues.

I opened #32315 before seeing this; it's the same mechanism from the opposite end, so I'll continue here and close mine as a duplicate.

This issue frames the switcher around a Light mode for small/local models. The same opt-in selector also solves the high-capability end — and #10927 (overspecification degrading reasoning in capable models), which is cited above, is exactly the case I have data for.

I prototyped a Frontier mode (the same idea as Light, just a different target): a prompt variant that pushes GPT/Claude-class models toward root-cause reasoning instead of "looks fine" conclusions. Measured with a within-session controlled A/B on a public code-review task (planetiler, last 10 commits, known seeded regressions) — same model, same agent prompt, same session, only the system prompt swapped:

bug (public-API silent semantic change)	baseline	frontier
reservoir polygon dropped	16.7%	62.5%
signed→unsigned comparison	16.7%	87.5%
compareTo ordering change	0%	50%
false positives	0	0

~45–71pp better recall at the same (zero) false-positive rate.

This reinforces the case for the switcher being a general mechanism rather than a single Light mode: the same option naturally carries Light (trim for small models) and Frontier (elevate for capable models), with Default unchanged.

I have a working branch for the Frontier end — the selector mechanism (~30 lines), two prompt files, unit tests, and an Apache-2.0 NOTICE for principles paraphrased from the Codex CLI prompts. Happy to adapt it to whatever config shape the maintainers prefer here (a mode/variant enum), or open a PR if there's interest in landing the mechanism with Default + one alternate to start.

This would be a very welcome improvement for our local infrastrukture.

My issue #39537 is a duplicate of this. I would like a config option to disable/replace system prompt in particular. Don't see any reason for prompts to be built-in, since Opencode is an open and highly customizable tools, in contrary to competitors.

Why not just let the user nuke everything from a certain agent session? Offering this OPENCODE_DISABLE_CLAUDE_CODE only as a global setting sort of diminishes this flag's capability.

There is a good chance a user might want all the circus and drama Calude Code has to offer on the same machine, esp. if it's a complex task (says a complex coding project or huge codebase, or both). But say another user (or the same user) at some point wants to just work with a few .txt/.md files in a directory and needs writing feedback, or so, it's absolutely bonkers in that case that OpenCode would still send something like git or node or whatever, unless the user completely shut that off via that flag.

I see issues closer to that have been closed before #1157 #5637

Thanks for the detailed proposal! You're asking for a system prompt mode setting (Default/Light, and possibly Custom later), so smaller or local models, and people who want minimal prompting, don't pay for the full built-in prompts. Maintainers will consider it.

In the meantime, in OpenCode v2 (2.x) the base system prompt is already short. Giving an agent its own prompt replaces the default prompt completely, and the model-specific prompts (e.g. for Claude or GPT) are then left out too:

{
  "agent": {
    "build": {
      "prompt": "{file:./prompts/minimal.txt}"
    }
  }
}

See the agent prompt docs: https://opencode.ai/docs/agents/#prompt

Related issues:

default system prompt materiallly freaks out / degrades reasoning of every high reasoning model #10927: overspecified prompts degrading reasoning in capable models
[FEATURE]: Remove hardcoded NEVER-commit rule from default/trinity system prompts #50579: removing a hardcoded rule from the default prompts
[FEATURE]: GUI for per-model profile/context parameters (system prompt, temperature, context window) #46153: per-model profiles, including the system prompt
Proposal: model-tier-specific system prompt variant behind an opt-in option #32315 and [FEATURE]: Allow disabling or replacing the built-in provider system prompt #39537: later requests that were pointed to this issue

Thanks for the suggestion. This isn't something we plan to build, so closing to keep the tracker focused.

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[FEATURE]: System prompt mode switcher (Default/Light) #15457

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[FEATURE]: System prompt mode switcher (Default/Light) #15457

Description

Feature hasn't been suggested before.

Describe the enhancement you want to request

Problem

Proposal

Configuration

Related issues

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m-nelly commented on Mar 3, 2026

okuyam2y commented on Jun 14, 2026

thekk1 commented on Jul 15, 2026

violog commented on Aug 1, 2026

justauserid commented on Sep 3, 2026

opencodejr commented on Oct 29, 2026

neriousy commented on Nov 12, 2026

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