# Use BigModel.io with LlamaIndex

> Connect LlamaIndex to BigModel.io with OpenAILike in Python or the OpenAI class in TypeScript, using https://bigmodel.io/v1. Set is_chat_model, context window, streaming and tools.

Web version: https://bigmodel.io/docs/llamaindex · Updated 2026-10-18

LlamaIndex reaches BigModel.io through its OpenAI-compatible LLM classes: `OpenAILike` in Python and `OpenAI` from `@llamaindex/openai` in TypeScript.

| Setting | Python (`OpenAILike`) | TypeScript (`OpenAI`) |
|---|---|---|
| Base URL | `api_base="https://bigmodel.io/v1"` | `baseURL: "https://bigmodel.io/v1"` |
| API key | `api_key=...` | `apiKey: ...` |
| Model | `model="glm-5.3"` | `model: "glm-5.3"` |
| Chat endpoint | `is_chat_model=True` (required) | default |

Copy model IDs from the [model catalog](https://bigmodel.io/models); availability depends on the key's group.

```bash
export BIGMODEL_API_KEY="sk-..."
```

## Install

```bash [Python]
pip install llama-index-llms-openai-like
```

```bash [TypeScript]
npm install llamaindex @llamaindex/openai
```

## Minimal call

```python [Python]
import os
from llama_index.llms.openai_like import OpenAILike

llm = OpenAILike(
    model="glm-5.3",
    api_base="https://bigmodel.io/v1",
    api_key=os.environ["BIGMODEL_API_KEY"],
    is_chat_model=True,
    is_function_calling_model=True,
    context_window=128000,  # set to the model's context window from its model page
)
print(llm.complete("Explain vector databases in three sentences."))
```

```ts [TypeScript]
import { OpenAI } from "@llamaindex/openai";

const llm = new OpenAI({
  model: "glm-5.3",
  apiKey: process.env.BIGMODEL_API_KEY,
  baseURL: "https://bigmodel.io/v1",
});

const res = await llm.chat({
  messages: [{ role: "user", content: "Explain vector databases in three sentences." }],
});
console.log(res.message.content);
```

`is_chat_model` defaults to `False`, which makes `OpenAILike` call the legacy `/v1/completions` endpoint. Always set it to `True`. Set `context_window` to the model's real window so LlamaIndex packs prompts correctly.

To use the model everywhere in LlamaIndex (query engines, agents), set it globally:

```python
from llama_index.core import Settings

Settings.llm = llm
```

## Streaming

```python [Python]
for chunk in llm.stream_complete("Write a haiku about latency."):
    print(chunk.delta, end="", flush=True)
```

```ts [TypeScript]
const stream = await llm.chat({
  messages: [{ role: "user", content: "Write a haiku about latency." }],
  stream: true,
});
for await (const chunk of stream) {
  process.stdout.write(chunk.delta);
}
```

## Tool calling (Python)

With `is_function_calling_model=True`, LlamaIndex sends OpenAI `tools`. Whether the model calls them depends on the model.

```python
from llama_index.core.tools import FunctionTool

def get_weather(city: str) -> str:
    """Get the current weather for a city."""
    return f"Sunny in {city}"

tool = FunctionTool.from_defaults(fn=get_weather)
print(llm.predict_and_call([tool], "What's the weather in Hangzhou?"))
```

## Verify the setup

Run the minimal call. A reply means the base URL and key work; the request should also appear in [Usage](https://bigmodel.io/usage) with endpoint `/v1/chat/completions`. If Usage shows nothing and you got a 404, `is_chat_model` is probably unset.

## Troubleshooting

**404 on every request (Python).** `is_chat_model` is `False`, so the call goes to `/v1/completions`. Set `is_chat_model=True`.

**404 on every request.** The base URL is missing `/v1`. Use `https://bigmodel.io/v1`.

**Prompts are truncated or "context window" errors.** `context_window` is left at its small default. Set it from the model page.

**401 `INVALID_API_KEY` or `API_KEY_REQUIRED`.** The key is empty in this process, or an `OPENAI_API_KEY` from your environment is used instead. Pass the key explicitly.

**503 `No available accounts: no available accounts supporting model: ...`.** The model ID is wrong or not in the key's group. Copy it from the [model catalog](https://bigmodel.io/models).

**403 `INSUFFICIENT_BALANCE` or 429.** Top up in [Billing](https://bigmodel.io/purchase); for 429 see [Limits & rate limits](https://bigmodel.io/docs/rate-limits).

## Related

- [OpenAI SDK](https://bigmodel.io/docs/openai-sdk-langchain)
- [LangChain](https://bigmodel.io/docs/langchain) and [Vercel AI SDK](https://bigmodel.io/docs/vercel-ai-sdk)
- [Tool calling](https://bigmodel.io/docs/tool-calling)