If your code is written against the OpenAI SDK, you can usually switch providers with one line. Below: what changes, what stays the same and where a migration most often trips.
What changes
Only the base URL and the key:
from openai import OpenAI
client = OpenAI(
base_url="https://api.codexkey.online/v1",
api_key="sk_cdx_your_key",
)
Everything else stays as it was: methods, message structure, stream handling, response parsing.
What does not change
The role-based message format, temperature and max tokens, streaming over server-sent events, the response shape with its choices array. Libraries written against OpenAI keep working.
Where it usually breaks
Model names. Identifiers differ between providers. A migration fails here more often than anywhere else, but the error is always clear: a 400.
Parameters that do not exist. Some provider-specific fields are not supported everywhere. If you used something exotic, check it separately.
A domain hardcoded in the source. Sometimes the base URL is not in config but written straight into the code, and in more than one place. Before you celebrate, grep the project for api.openai.com.
A two-minute check
The quickest way to confirm the connection works:
curl https://api.codexkey.online/v1/chat/completions \
-H "Authorization: Bearer $KEY" \
-H "Content-Type: application/json" \
-d '{"model":"claude-sonnet-5","messages":[{"role":"user","content":"say ok"}]}'
If a response comes back, whatever is left to break is model names and provider-specific parameters.
Why this matters when choosing a provider
Compatibility works in both directions: it is easy to arrive at a provider and just as easy to leave. A provider that forces you to rewrite code into its own format holds you by the cost of switching, not by quality.
That is why we keep both formats on one codexkey endpoint, Anthropic Messages and OpenAI Chat Completions. Code written against it works with other providers too.
In short
Change the base URL and the key, then check model names. If the code used a standard SDK, migration takes minutes, not a sprint.