The problem with deepseek-reasoner in OpenCode

[kirinchin156-source]

Description

Questions for OpenCode Developers:

1. "Does OpenCode support the full reasoning_content cycle for DeepSeek thinking mode?"
2. "Are there plans to implement saving reasoning chains between tool calls?"
3. "Is there a workaround for using deepseek reasoner with Shell tools?"

Plugins

No response

OpenCode version

No response

Steps to reproduce

No response

Screenshot and/or share link

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Operating System

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Terminal

No response

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• DeepSeek V3.2 : reasoning_content not cleared from message history on new turns, causing excess token usage and violating API spec #5577: DeepSeek V3.2 reasoning_content not cleared from message history on new turns, causing excess token usage and violating API spec
• Deepseek v3.2 - Azure Foundry - It works partially, tools and todos not. #6615: Deepseek v3.2 - Azure Foundry - It works partially, tools and todos not
• reasoning_content not sent when using @ai-sdk/openai-compatible with deepseek-reasoner #6040: reasoning_content not sent when using @ai-sdk/openai-compatible with deepseek-reasoner (closed)

Feel free to ignore if your specific case is not addressed by these issues.

[Robinblennert]

Have you fixed it yet?
I used 128k really quick and couldnt save the work. Crazy NO idea how much of tokens was used but I understand there is a bug.

[tongsh6]

I can reproduce a very similar issue with a custom subagent using deepseek/deepseek-reasoner in OpenCode.

Setup

Custom local subagent:

~/.config/opencode/agents/architect.md

This is not an oh-my-opencode built-in agent. It is a local custom OpenCode subagent.

Observed error

When this subagent performs tool-using work, OpenCode fails with:

Why this seems like an OpenCode compatibility issue

According to DeepSeek's official docs for thinking mode + tool calls:

• during the same reasoning/tool-call turn, the client must send the assistant message back with:
  • content
  • reasoning_content
  • tool_calls

Docs:
https://api-docs.deepseek.com/guides/thinking_mode#tool-calls

This suggests OpenCode is likely dropping reasoning_content when replaying assistant/tool history for reasoning models during tool-call continuation.

Related notes

• I also found anomalyco/opencode#9397, which looks closely related
• This does not appear to be caused by the agent prompt itself
• It seems specific to:
  • reasoning model
  • tool calls
  • assistant history replay

Helpful distinction

This may be reproducible specifically with:

• custom subagent
• deepseek/deepseek-reasoner
• tools enabled (bash: true was enough in my case)

Temporary workaround on my side is to switch this subagent to deepseek/deepseek-chat or a non-DeepSeek reasoning model.

If useful, I can provide a more minimal repro prompt next.

[tongsh6]

Follow-up: my previous comment lost the fenced blocks due to shell quoting. Here is the exact missing content.

Local subagent config

---
description: Read-only architecture review agent
mode: subagent
model: deepseek/deepseek-reasoner
temperature: 0.1
steps: 16
tools:
  write: false
  edit: false
  bash: true
---

Exact error text

Missing reasoning_content field in the assistant message at message index 32.
For more information, please refer to https://api-docs.deepseek.com/guides/thinking_mode#tool-calls

This happened while the custom subagent was doing tool-using work.

[tongsh6]

Solution:

Configure the DeepSeek model with:

{
  "provider": {
    "deepseek": {
      "npm": "@ai-sdk/openai-compatible",
      "name": "DeepSeek",
      "options": {
        "baseURL": "https://api.deepseek.com/v1",
        "apiKey": "{env:DEEPSEEK_API_KEY}"
      },
      "models": {
        "deepseek-reasoner": {
          "name": "DeepSeek Reasoner",
          "interleaved": {
            "field": "reasoning_content"
          }
        }
      }
    }
  }
}

The key part is:

"interleaved": {
  "field": "reasoning_content"
}

After adding this and restarting OpenCode, the issue was resolved.