Per-Model Instructions

I've been trying out GPT-5, and it needs very different behavioural instructions compared to the Anthropic models. It would be really nice if the "instructions" files defined in the config could be defined per provider/model, so that we can switch between models and they'll pick up the relevant instructions without having to edit the config file.

There actually are different system prompts for some models. GPT-5 uses the packages/opencode/src/session/prompt/codex.txt

@nefthy

I completely support this feature request!
There should be the possibility to use custom prompts, maybe on an agent level?

Currently there is a differentiation based on the model name:

https://github.com/sst/opencode/blob/dev/packages/opencode/src/session/system.ts#L24

import PROMPT_COPILOT_GPT_5 from "./prompt/copilot-gpt-5.txt"
[...]

  export function provider(modelID: string) {
    if (modelID.includes("gpt-5")) return [PROMPT_COPILOT_GPT_5]
    if (modelID.includes("gpt-") || modelID.includes("o1") || modelID.includes("o3")) return [PROMPT_BEAST]
    if (modelID.includes("gemini-")) return [PROMPT_GEMINI]
    if (modelID.includes("claude")) return [PROMPT_ANTHROPIC]
    return [PROMPT_ANTHROPIC_WITHOUT_TODO]
  }

So IMHO for GPT-5 copilot-gpt-5.txt is used and not codex.txt (which is in my opinion not used at all at the moment).
@nefthy: can you please check?

@giddie

I think what @giddie is getting at is that instructions: in your config should allow you to specify which models you want to load the instruction for.

makes sense, some models behave differently than others

@florath

@florath yes you are right. It has changed since I last checked it :)

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Per-Model Instructions #1891

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nefthy commented on Aug 13, 2025

florath commented on Aug 14, 2025

rekram1-node commented on Aug 14, 2025

nefthy commented on Aug 14, 2025

rekram1-node commented on Dec 28, 2025

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