moonshot AI kimi k2 all get error.

[magic-thomas]

Description

Hello.

Moonshot AI can not be used for now.

Invalid request: the message at position 5 with role 'assistant' must not be empty

all Kimi K2 models shows same error.

OpenCode version

1.0.193

Steps to reproduce

No response

Screenshot and/or share link

No response

Operating System

No response

Terminal

No response

[github-actions]

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

• Groq Kimi K2 Caching #2174: Groq Kimi K2 Caching - caching-related issues with Kimi K2
• Kimi K2 cache not working on Zen #3172: Kimi K2 cache not working on Zen - similar caching problems with Kimi K2

The error about empty assistant messages in the conversation history is a known issue affecting Kimi K2 models. Feel free to ignore if none of these address your specific case.

[rekram1-node]

Can you share a session?

opencode export > session.json

[magic-thomas]

It is working now..

and I can see GLM 4.7 on the model list just now.

Maybe something happened during models updating..

Thanks.

[jukofyork]

Leaving this here in case anybody else has this same error as it seems to be the top/only hit for this when you search...

---

If you cancel a tool call you can sometimes end up with a blank/empty assistant message which then causes errors like this for the Moonshot AI provider on openrouter, eg:

{
  "responseBody": {
    "error": {
      "message": "Provider returned error",
      "code": 400,
      "metadata": {
        "raw": {
          "error": {
            "message": "Invalid request: the message at position XXX with role 'assistant' must not be empty",
            "type": "invalid_request_error"
          }
        },
        "provider_name": "Moonshot AI",
        "is_byok": false
      }
    },
    "user_id": "user_xxx"
  },
  "isRetryable": false,
  "data": {
    "error": {
      "message": "Provider returned error",
      "code": 400
    }
  }
}

NOTE: To find the actual error you have to look in the log file as in the TUI you just get a cryptic red "Provider Error" or similar!

I couldn't get the normal opencode plug-in hooks to catch and fix this, but did manage to monkey-patch it like this:

/**
 * FixEmptyAssistantMessages Plugin
 * 
 * PROBLEM:
 * Moonshot AI (and some other providers) reject API calls with empty assistant messages,
 * returning: "Invalid request: the message at position X with role 'assistant' must not be empty"
 * 
 * ATTEMPTED SOLUTIONS THAT FAILED:
 * 1. Plugin hooks (message.updated, message.part.updated, event) - These operate at the 
 *    session/database layer, but the empty messages are created AFTER hooks fire and 
 *    BEFORE the HTTP request is sent to the provider. The plugin system doesn't expose 
 *    the provider transform layer where filtering needs to happen.
 * 
 * 2. Removing ALL empty assistant messages - This broke tool call chains because 
 *    subsequent "tool" role messages reference the tool_call_id from the assistant 
 *    messages. Removing them caused "tool_call_id is not found" errors.
 * 
 * SOLUTION:
 * Monkey-patch global.fetch to intercept the API request body and filter messages 
 * at the HTTP layer. This is the only layer where we can see the final message array 
 * being sent to the provider.
 * 
 * KEY INSIGHT:
 * Empty content (null/undefined/"") is acceptable to Moonshot IF the assistant message 
 * has tool_calls. Only messages with BOTH empty content AND no tool_calls need to be 
 * removed - these are "orphaned" empty messages that serve no purpose.
 */

export const FixEmptyAssistantMessages = async () => {      
  const originalFetch = globalThis.fetch;
  
  globalThis.fetch = async (url, options) => {
    const urlStr = typeof url === 'string' ? url : url.toString();
    
    if (urlStr.includes('openrouter') && options?.body) {
      try {
        const body = JSON.parse(options.body);
        
        if (body.messages) {
          const before = body.messages.length;
          
          body.messages = body.messages.filter(msg => {
            // Only remove empty assistant messages WITHOUT tool_calls
            if (msg.role !== 'assistant') return true;
            
            const content = msg.content;
            const hasToolCalls = msg.tool_calls?.length > 0;
            
            const isEmpty = 
              !content || 
              (typeof content === 'string' && content.trim() === '') ||
              (Array.isArray(content) && content.length === 0);
            
            // Keep if has tool_calls, remove only if truly empty/orphaned
            return !(isEmpty && !hasToolCalls);
          });
          
          if (body.messages.length !== before) {
            options = { ...options, body: JSON.stringify(body) };
          }
        }
      } catch (e) {}
    }
    
    return originalFetch(url, options);
  };
  
  return {};
};

To use just copy to ~/.config/opencode/plugins.

It probably manifests itself for the official Moonshot API too so it might be worth widening the urlStr.includes('openrouter') test.

There are a a lot of other PRs related to this for other providers:

#2651
#14586

so it would probably be better to fix this in the code ultimately, but at least this seems to work for now.