Direct answer
How do I use one API for multiple LLMs?
Connect an OpenAI- or Anthropic-compatible client to an AI gateway, authenticate with a gateway key, and set the model to a canonical ID from its live catalog. Keep the endpoint family and model ID configurable, because specialized modalities and model-specific features may require different routes.
Last reviewed 2026-08-15 · Editorial review: KeepRouter Editorial
1. Pick the client contract
Use OpenAI Chat Completions or Responses when your application is built around OpenAI-shaped objects. Use Anthropic Messages for an Anthropic SDK or Claude Code workflow. Do not translate between them inside every feature; centralize the chosen client shape at your platform boundary.
2. Prove authentication
Create a key restricted to the current free model, change the base URL, and send a bounded non-streaming request. Inspect the request record before adding paid credit. This separates connection problems from model-selection problems.
3. Build an approved model map
Read the live catalog, choose IDs that support the required endpoint, and record the capability tests each passed. Keep those IDs in configuration. A public catalog is not automatically your product's approved catalog.
4. Run the same workload
Use a fixed prompt, context, tool set, output cap, and pass criteria. Compare completion, input and output tokens, charge, latency, and product quality. Changing only the model ID makes the integration comparable; it does not make the outputs equivalent.
5. Put boundaries on production
Issue separate keys per environment or service, set model allowlists and spend limits, handle retryable errors deliberately, and retain a tested rollback. For images, embeddings, audio, or other specialized modalities, use the endpoint listed on the model page instead of forcing everything through chat.
Minimal shape
model = os.environ["APPROVED_MODEL_ID"]
client = OpenAI(base_url="https://keeprouter.com/v1", api_key=os.environ["KEEPROUTER_KEY"])
response = client.chat.completions.create(model=model, messages=messages, max_tokens=800)Frequently asked questions
Can I switch models by changing one field?
Often yes when both models support the same route, but you must still test behavior and capabilities.
Should every model share one key?
A gateway key can access multiple approved IDs, but production keys should use a narrow allowlist.
Can chat routes serve images and audio?
Specialized generation or audio operations normally use their own documented endpoints.
Where should model IDs live?
Keep them in reviewed deployment configuration so promotion and rollback do not require code changes.