A Well-Chosen Base URL Keeps SDK Changes Small

A base URL changes the request destination

The OpenAI Node SDK gives a Node.js application convenient methods for sending model requests. By default, those requests go to OpenAI. A base URL changes that destination, allowing the same SDK to contact another service that supports the relevant OpenAI API format.

This is a routing setting, not a model setting. It tells the client where to send a request, while the model field tells the receiving service which model you want. Keeping those responsibilities separate makes the setup easier to understand and troubleshoot.

For newcomers, the useful finding is that changing destinations can require very little application work. However, a successful connection does not prove that every endpoint, parameter, or streaming feature behaves identically.

The client constructor accepts your destination setting

When creating an OpenAI client, supply the destination through the option named baseURL. The capitalization matters. Set the API key for that destination on the same client so the address and credentials stay together.

The SDK also supports the OPENAI_BASE_URL environment variable. This can be useful when development and production use different destinations without changing application logic. An explicitly supplied constructor option takes precedence over that environment variable, so check both places if requests reach an unexpected service.

Use the exact SDK-compatible base address documented by your destination. A service’s public API address and its OpenAI-compatible base may differ in their version segment. Do not guess whether that segment belongs in the address, and do not enter a complete endpoint address where the SDK expects a base.

The destination and API key belong together

A relay generally expects a key issued by that relay, rather than an OpenAI account key. Treat the destination and its credential as one configuration pair. Mixing them commonly produces authentication failures even when the rest of the request is correct.

Keep credentials in a server-side environment or secret manager. Do not embed them in browser code, commit them to source control, or include them in debugging screenshots. Changing the base URL also changes which service receives your prompts and responses, so review that service’s privacy and retention terms before sending sensitive information.

Shared SDK syntax does not guarantee identical features

An OpenAI-compatible service can accept familiar request shapes without implementing the entire OpenAI API. Before moving an application, confirm support for the particular endpoint and features it uses. Streaming, tool calls, structured outputs, and multimodal inputs deserve individual checks.

Model identifiers also come from the destination’s documentation. A recognizable display name is not necessarily the exact identifier accepted by its API. Begin with a small text request, then test more demanding behavior separately. This makes it easier to distinguish an address problem from an unsupported feature.

A relay adds routing choices without replacing verification

BestRelay, which publishes this article, is a quality-first API relay that forwards each request to the official model named in it, without substitution. Its coverage includes Claude, GPT, Gemini, DeepSeek, Kimi, GLM, Qwen, Grok, and more.

It works with Claude Code, Codex, Gemini CLI, and OpenAI SDKs, although each tool has its own connection settings. Billing is pay-as-you-go using provider-reported token counts, with cache reads and writes priced separately. Members also earn referral commission when people they invite top up. Create a BestRelay account when you are ready to try it.

A small connection test prevents larger debugging sessions

After setting the base URL and key, send one short request using a documented model identifier. Check that authentication succeeds and the response has the structure your application expects. Then test streaming or other required capabilities before increasing traffic.

If the request fails, inspect the destination, credentials, model identifier, and endpoint support before rewriting application logic. Once the connection works, review timeouts and retry behavior for your workload. A base URL keeps the client change small; careful validation makes that small change dependable.