reasoning_content is missing when using DeepSeek V4 Flash in thinking

[beeckrumi0000]

Description

Summary

When using OpenCode with OpenRouter and DeepSeek V4 Flash/Pro, the agent fails with:
[DeepSeek] The 'reasoning_content' in the thinking mode must be passed back to the API.

Environment

• OpenCode: latest
• OpenRouter: latest
• Model: DeepSeek V4 Flash / DeepSeek V4 Pro
• reasoningEffort: xhigh
• Thinking mode: enabled

Expected behavior

OpenCode should preserve and pass reasoning_content back to the API when the model requires it.

Actual behavior

The request fails because reasoning_content is missing from the payload.

Notes

This also happens with DeepSeek V4 Pro on OpenRouter, not only Flash.
I confirmed this happens with OpenCode + OpenRouter + DeepSeek V4 Flash/Pro even after updating to the latest version.

Reference

The issue seems related to reasoning field propagation in OpenCode/OpenRouter integrations.

Plugins

warp

OpenCode version

1.15.11

Steps to reproduce

No response

Screenshot and/or share link

Operating System

Ubuntu 22.04

Terminal

Warp

[github-actions]

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

• DeepSeek thinking mode: reasoning_content not passed back for tool call turns, causing 400 errors #24722: DeepSeek thinking mode: reasoning_content not passed back for tool call turns, causing 400 errors
• [BUG] DeepSeek reasoning_content not preserved across tool calls, causing HTTP 400 error #28945: [BUG] DeepSeek reasoning_content not preserved across tool calls, causing HTTP 400 error
• DeepSeek V4: reasoning_content 400 error persists on v1.14.31 — complete fix exists in unmerged PRs #25311: DeepSeek V4: reasoning_content 400 error persists on v1.14.31 — complete fix exists in unmerged PRs
• Bug: DeepSeek reasoning_content missing on session continuation (v1.15.7) #28716: Bug: DeepSeek reasoning_content missing on session continuation (v1.15.7)
• thinking is enabled but reasoning_content is missing in assistant tool call message at index ... #25758: thinking is enabled but reasoning_content is missing in assistant tool call message at index ...
• deepseek V4 flash 或者pro 出现 链接中断 ，中断后 再也不能正常对话工作了Error from provider (DeepSeek): The reasoning_content in the thinking mode must be passed back to the API. #24920: deepseek V4 flash/pro — same error message about reasoning_content not passed back
• DeepSeek V4 Pro SiliconFlow Bad Request: The reasoning_content in the thinking mode must be passed back to the API. #28974: DeepSeek V4 Pro SiliconFlow — same error: reasoning_content in thinking mode must be passed back

These existing issues cover the same root cause (reasoning_content not preserved/passed back when using DeepSeek thinking mode). Consider adding a "+1" or additional context to one of those instead.

[0zKillua]

1. is this issue specific to openrouter+deepseek combination?
2. Why is it not fixed? what's the work around for time being?

[panzeyu2013]

I think this issue is indeed specific to openrouter. I found similar errors when using New API.

[ButlerJoseph]

As a workaround I set my opencode config to this #25086 (comment)

[vinaysb]

As a workaround I set my opencode config to this #25086 (comment)

Are you also using the same provider, i.e. siliconflow? I am using the deepseek provider and wonder if its some change on the provider side

[bixycler]

This is specific to OpenRouter in my case: I see OpenCode shows thinking options and returns thinking content to the API for the official DeepSeek provider as well as the DeepSeek model in OpenCode Zen, but not for DeepSeek models via OpenRouter.

No thinking options for DeepSeek V4 Flash via OpenRouter: (Note the OpenRouter icon at the model name)

Show thinking options for DeepSeek V4 Flash via official provider: (Note the DeepSeek icon at the model name)

[bixycler]

As a workaround I set my opencode config to this #25086 (comment)

This workaround doesn't work for me: still the error of missing reasoning_content, and no thinking effort choices are shown!