DeepSeek V4 inherits conflicting default system prompt #38234

Description

DeepSeek V4 currently falls through to the generic default.txt system prompt. That prompt combines aggressive brevity rules (fewer than 4 lines, One word answers are best, and stopping immediately after edits) with guidance to delegate routine file search to the Task tool.

For DeepSeek V4 coding sessions this produces shallow responses and unnecessary subagent delegation. DeepSeek V4 should use a dedicated, consistent prompt that prefers direct read/grep/glob exploration and does not impose those conflicting response constraints.

Plugins

None

OpenCode version

1.18.4

Steps to reproduce

1. Configure a DeepSeek V4 model.
2. Start a coding task that requires reading and modifying several files.
3. Observe that the model receives the generic prompt's extreme brevity and Task-first file-search instructions.

Screenshot and/or share link

No response

Operating System

macOS 26.5.2

Terminal

No response