[Bug] DeepSeek V4 fails with 'reasoning_content must be passed back' error in multi-turn conversations

Bug Description

When using DeepSeek V4 with OpenCode, multi-turn conversations fail with the error:

The reasoning_content in the thinking mode must be passed back to the API

Steps to Reproduce

Configure DeepSeek V4 in opencode.json:

"deepseek": {
  "npm": "@ai-sdk/openai-compatible",
  "name": "DeepSeek",
  "options": {
    "baseURL": "https://api.deepseek.com",
    "apiKey": "sk-xxx"
  },
  "models": {
    "deepseek-reasoner": {
      "name": "DeepSeek-V4",
      "limit": {
        "context": 1048576,
        "output": 262144
      }
    }
  }
}

Start a conversation with DeepSeek V4
Send a second message in the same conversation
Error occurs

Expected Behavior

Multi-turn conversations should work seamlessly, with reasoning_content properly preserved between turns.

Actual Behavior

The conversation fails because @ai-sdk/openai-compatible doesn't preserve reasoning_content from DeepSeek's thinking mode responses.

Environment

OpenCode version: Latest
DeepSeek model: deepseek-reasoner (V4)
SDK: @ai-sdk/openai-compatible

Root Cause

DeepSeek V4 enables thinking mode by default and returns reasoning_content in responses. The OpenAI-compatible SDK doesn't handle this field, causing it to be lost between conversation turns.

Workaround

Switch to Anthropic API format, which natively supports reasoning modes:

"deepseekv4": {
  "npm": "@ai-sdk/anthropic",
  "name": "DeepSeek",
  "options": {
    "baseURL": "https://api.deepseek.com/anthropic",
    "apiKey": "sk-xxx"
  },
  "models": {
    "deepseek-v4-pro": {
      "name": "DeepSeek-V4-Pro",
      "limit": {
        "context": 1048576,
        "output": 262144
      },
      "options": {
        "thinking": {
          "type": "enabled",
          "budgetTokens": 8192
        }
      }
    }
  }
}

This configuration:

Uses @ai-sdk/anthropic instead of @ai-sdk/openai-compatible
Points to DeepSeek's Anthropic-compatible endpoint
Properly preserves reasoning_content across conversation turns
Allows explicit thinking mode configuration

Alternative Solutions

Community members have also suggested using transformRequestBody hooks to manually preserve reasoning_content, but the Anthropic API approach is cleaner and officially supported.

References

DeepSeek API docs: https://api-docs.deepseek.com/
Community discussion: feat (docs): add link to storage section vercel/ai#4768

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

DeepSeek thinking mode: reasoning_content must be passed back to API on conversation continuation #24104: DeepSeek thinking mode: reasoning_content must be passed back to API on conversation continuation (same error, same root cause)
Support DeepSeek V4 Thinking Mode with reasoning_content handling #24114: Support DeepSeek V4 Thinking Mode with reasoning_content handling (same model, same issue)
The reasoning_content in the thinking mode must be passed back to the API. #24083: The reasoning_content in the thinking mode must be passed back to the API (closed, exact same error message)
Missing reasoning_content field in the assistant message for DeepSeek API implementation #17523: Missing reasoning_content field in the assistant message for DeepSeek API implementation (same underlying problem)

roadmap: #214 filed — ChunkDelta and ChatMessage in openai_compat.rs …

  "provider": {
    "deepseek": {
      "models": {
        "deepseek-v4-flash": {
          "interleaved": {
            "field": "reasoning_content"
          }
        },
        "deepseek-v4-pro": {
          "interleaved": {
            "field": "reasoning_content"
          }
        }
      }
    }
  }

adding this to opencode.json fixes it

roadmap: #214 filed — ChunkDelta and ChatMessage in openai_compat.rs …

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[Bug] DeepSeek V4 fails with 'reasoning_content must be passed back' error in multi-turn conversations #24124

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[Bug] DeepSeek V4 fails with 'reasoning_content must be passed back' error in multi-turn conversations #24124

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Bug Description

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Expected Behavior

Actual Behavior

Environment

Root Cause

Workaround

Alternative Solutions

References

Activity

github-actions commented on Apr 24, 2026

lfaoro commented on Apr 27, 2026

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