[BUG] Claude Code changes model identifier mid-conversation on AWS Bedrock (eu to us region)

I think I am encountering a similar bug on Linux for bedrock as well. I think the issue specifically is that the model for the Task tool subagent doesn't respect the model set in the settings. Can you confirm if this is what you are seeing as well?

@dimohammed328 it totally makes sense that this would be caused by a subagent as that would explain the ability to resume the conversation with --resume. How can I verify that the Task tool causes the issue?

Unsure, if you're running into the issue, you can check if the last thing claude did was call a Task tool. I think you can also ask claude to do something as a subagent task so that would work as well.

I can confirm the issue, when a new Task spins up it uses the wrong model name:

> create a new subagent to document this package

⏺ I'll create a specialized agent to document this package. Let me launch a general-purpose agent to analyze the codebase and create comprehensive documentation.
  ⎿  API Error (500 {"error":{"message":"{\"message\":\"The provided model identifier is invalid.\"}. Received Model Group=us.anthropic.claude-sonnet-4-20250514-v1:0\nAvailable Model Group Fallbacks=None\nError doing the fallback: list index out of range","type":"None","param":"None","code":"500"}}) · Retrying in 1 seconds… (attempt 1/10)
  ⎿  API Error (500 {"error":{"message":"{\"message\":\"The provided model identifier is invalid.\"}. Received Model Group=us.anthropic.claude-sonnet-4-20250514-v1:0\nAvailable Model Group Fallbacks=None\nError doing the fallback: list index out of range","type":"None","param":"None","code":"500"}}) · Retrying in 1 seconds… (attempt 2/10)
  ⎿  API Error (500 {"error":{"message":"{\"message\":\"The provided model identifier is invalid.\"}. Received Model Group=us.anthropic.claude-sonnet-4-20250514-v1:0\nAvailable Model Group Fallbacks=None\nError doing the fallback: list index out of range","type":"None","param":"None","code":"500"}}) · Retrying in 2 seconds… (attempt 3/10)

⏺ Task(Document DNA package)
  ⎿  Initializing…

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/4855
2. https://github.com/anthropics/claude-code/issues/3903
3. https://github.com/anthropics/claude-code/issues/4264

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🤖 Generated with Claude Code

Here's a simple Node.js script that works around the issue for now. Set TARGET_URL to your LiteLLM instance (or point directly to Bedrock) by automatically modifying the url to point to the EU model.

Invoke Claude Code by starting the script then setting ANTHROPIC_BEDROCK_BASE_URL=http://localhost:8888/bedrock

ANTHROPIC_SMALL_FAST_MODEL=eu.anthropic.claude-3-5-haiku-20241022-v1:0 ANTHROPIC_MODEL=eu.anthropic.claude-sonnet-4-20250514-v1:0 ANTHROPIC_AUTH_TOKEN=sk-LITELLM_TOKEN ANTHROPIC_BEDROCK_BASE_URL=http://localhost:8888/bedrock CLAUDE_CODE_SKIP_BEDROCK_AUTH=1 CLAUDE_CODE_USE_BEDROCK=1 CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1 claude

import http from 'http';

const PORT = process.env.PORT || 8888;
const TARGET_URL = 'https://litellm.your-company.com';

const server = http.createServer(async (req, res) => {
  try {
    let targetPath = req.url;
    const usModelPattern = /us\.anthropic\.claude-[^\/]+/g;
    
    if (usModelPattern.test(targetPath)) {
      const originalPath = targetPath;
      targetPath = targetPath.replace(/us\.anthropic\./g, 'eu.anthropic.');
      console.log(`\n🔄 Model redirect: US -> EU`);
      console.log(`  Original: ${originalPath}`);
      console.log(`  Rewritten: ${targetPath}`);
    }
    
    const targetUrl = `${TARGET_URL}${targetPath}`;
    
    const chunks = [];
    for await (const chunk of req) {
      chunks.push(chunk);
    }
    const body = Buffer.concat(chunks);
    
    console.log(`\n--- ${new Date().toISOString()} ---`);
    console.log(`${req.method} ${targetPath}`);

    if (body.length > 0) {
      const bodyString = body.toString('utf-8');
      
      try {
        const jsonBody = JSON.parse(bodyString);
        // Check if model is also specified in the body and replace it
        if (jsonBody.model && jsonBody.model.includes('us.anthropic.')) {
          const originalModel = jsonBody.model;
          jsonBody.model = jsonBody.model.replace('us.anthropic.', 'eu.anthropic.');
          console.log(`  Body model redirect: ${originalModel} -> ${jsonBody.model}`);
          // Update the body with the modified JSON
          body.length = 0;
          const newBodyString = JSON.stringify(jsonBody);
          const newBody = Buffer.from(newBodyString, 'utf-8');
          Object.assign(body, newBody);
        }
      } catch (e) {
      }
    }
    
    const headers = { ...req.headers };
    delete headers['host'];
    delete headers['content-length']; // Let fetch calculate this
    
    // Make the proxied request
    const response = await fetch(targetUrl, {
      method: req.method,
      headers: headers,
      body: body.length > 0 ? body : undefined,
      redirect: 'manual'
    });
    
    // Log response status
    //console.log(`Response: ${response.status} ${response.statusText}`);
    
    res.statusCode = response.status;
    res.statusMessage = response.statusText;
    
    response.headers.forEach((value, key) => {
      if (!['content-encoding', 'transfer-encoding'].includes(key.toLowerCase())) {
        res.setHeader(key, value);
      }
    });
    
    const responseBody = await response.arrayBuffer();
    res.end(Buffer.from(responseBody));
    
  } catch (error) {
    console.error('Proxy error:', error);
    res.statusCode = 500;
    res.setHeader('Content-Type', 'application/json');
    res.end(JSON.stringify({ 
      error: 'Proxy error', 
      message: error.message 
    }));
  }
});

server.listen(PORT, () => {
  console.log(`Proxy server running on http://localhost:${PORT}`);
  console.log(`Forwarding requests to: ${TARGET_URL}`);
  console.log('Ready to accept requests...');
  console.log('\n✨ Auto-redirecting US models to EU models');
});

// Handle server errors
server.on('error', (error) => {
  console.error('Server error:', error);
});

// Graceful shutdown
process.on('SIGINT', () => {
  console.log('\nShutting down proxy server...');
  server.close(() => {
    console.log('Server closed');
    process.exit(0);
  });
});

process.on('SIGTERM', () => {
  console.log('\nShutting down proxy server...');
  server.close(() => {
    console.log('Server closed');
    process.exit(0);
  });
});

Same issue here. Multiple tools affected by invalid model identifier error:

Tools failing:

• Task tool (subagents): `API Error

(us.anthropic.claude-sonnet-4-20250514-v1:0): 400 The provided model identifier is invalid.`

Environment:

• Claude Code 1.0.88
• macOS
• /model shows correct:

apac.anthropic.claude-sonnet-4-20250514-v1:0

Tools are using wrong us. prefix instead of apac.. Breaks entire subagent system.

https://github.com/anthropics/claude-code/issues/4855#issuecomment-3220160458

Undocumented CLAUDE_CODE_SUBAGENT_MODEL env var works for me. (v1.0.92)

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Still occurring

This would be nice if it got fixed!

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