GLM-5 405 Error Explained: Why It Happens and How to Fix It Fast

If you’ve ever seen the HTTP 405 Method Not Allowed error while trying to connect to GLM-5 via the Nano-GPT proxy, you know how frustrating it can be. This error often appears when your code attempts to reach the API but gets rejected before the model even receives your prompt. The good news is that this is almost always a configuration issue that is easy to fix.

Quick Answers: Why Does This Happen?

• Trailing Slashes: You likely added a / at the end of your Base URL (e.g., .../api/v1/). This causes a redirect that downgrades your request from POST to GET, which the API rejects.
• Wrong HTTP Method: Your code might be sending a GET request to an endpoint that requires POST.
• Socket Timeouts: For long-thinking models like GLM-5, a connection timeout (ECONNRESET) can sometimes trigger an automatic retry that functions as a malformed GET request.

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Why This Error Occurs

The logic behind the 405 Method Not Allowed error is straightforward but strict. Nano-GPT (like OpenAI) uses a REST API structure that separates actions:

• GET is used for reading data (like listing available models).
• POST is used for sending data (like sending a chat prompt to generate text).

When you ask the API to generate text (a “Chat Completion”), you must use POST. If your application accidentally sends a GET request to that endpoint—or if a network redirect turns your POST into a GET—the server blocks it immediately.

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Fix 1: Check Your Base URL (Most Common Fix)

The most common trigger for this error is a tiny typo in the Base URL.

If your URL ends with a slash (/), the server tries to “fix” it by redirecting you to the version without the slash. Unfortunately, many HTTP libraries (like Python’s requests or generic fetch wrappers) automatically switch to a GET request when following this redirect, causing the error.

What NOT to Do:

• Don’t use: https://nano-gpt.com/api/v1/
• Don’t use: https://nano-gpt.com/api/v1/chat/completions (The SDK usually adds the path for you)

How to Fix It:
Ensure your Base URL is exactly this string, with no trailing slash:

https://nano-gpt.com/api/v1

Python Example

If you are using the OpenAI Python SDK, initialize your client like this:

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_NANO_GPT_API_KEY",
    # Correct: No trailing slash
    base_url="https://nano-gpt.com/api/v1"
)

OpenHands Configuration

If you are using OpenHands (or similar agent tools):

1. Go to Settings → LLM Configuration.
2. Toggle on Advanced.
3. Set Base URL to: https://nano-gpt.com/api/v1
4. Set Model to: openai/zai-org/glm-5 (The specific prefix helps some tools route correctly).

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Fix 2: Enforce POST in Custom Scripts

If you aren’t using an SDK and are writing your own raw API calls (using fetch in JavaScript or requests in Python), your code might be defaulting to GET if you don’t specify otherwise.

You must explicitly set the method to POST.

JavaScript / Node.js Example:

const response = await fetch("https://nano-gpt.com/api/v1/chat/completions", {
    method: 'POST', // This line is mandatory
    headers: {
        'Authorization': `Bearer ${API_KEY}`,
        'Content-Type': 'application/json'
    },
    body: JSON.stringify({
        model: "zai-org/glm-5",
        messages: [{role: "user", "content": "Hello"}]
    })
});

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Fix 3: Handle Timeouts and Retries

GLM-5 is a massive “Mixture-of-Experts” model. When you use the “Thinking Mode” variant (zai-org/glm-5-original:thinking), it can take a long time to start generating text because it is processing complex logic.

If your connection times out while waiting (often seen as a “Socket Hang Up” or ECONNRESET), your app might automatically try to reconnect. Some apps do a quick “check” (a ping) to see if the server is there. This “check” is often a GET request, which triggers the 405 error.

To prevent this:

• Enable Streaming: Streaming sends data in small chunks rather than waiting for the whole answer. This keeps the connection alive and prevents timeouts.
• Increase Timeout Settings: If your client allows it, increase the read timeout to at least 60–120 seconds.

Python Streaming Example:

response = client.chat.completions.create(
    model="zai-org/glm-5",
    messages=[{"role": "user", "content": "Analyze this code..."}],
    stream=True  # Keeps connection active
)

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Correct Model Names

Using the wrong model ID won’t usually cause a 405, but it can cause other routing issues that look similar. Make sure you are using the official Nano-GPT identifiers for GLM-5:

• Standard: zai-org/glm-5
• Thinking Mode: zai-org/glm-5-original:thinking (Set temperature to 1.0 for this model)

Conclusion

The HTTP 405 error essentially means you are trying to “read” an endpoint that is only meant to be “written” to. To solve it, sanitize your Base URL by removing the trailing slash, ensure your code explicitly uses POST, and enable streaming for long-context tasks.

1. Check the URL: Ensure it is strictly https://nano-gpt.com/api/v1.
2. Force POST: Verify your HTTP headers and methods.
3. Stream data: Prevent timeouts that lead to bad retry loops.