Open Responses API Format With an LLM Provider

The Open Responses API format gives applications a consistent way to send prompts to an LLM provider and receive structured response events. To use it, you need a provider or gateway that supports the format, its endpoint and authentication details, and a client that can send the expected request and handle the returned response.

What You’ll Need

• A compatible provider or gateway: Confirm that it supports the Open Responses API format, not merely a similarly named endpoint or another provider’s API.
• Connection details: Get the base URL, the route for creating responses, an API key or other required credentials, and the model identifier from your provider’s documentation.
• A client: You can use an HTTP library, an SDK that explicitly supports the format, or a command-line tool such as curl. Check compatibility before assuming a provider-specific SDK uses the same request schema.
• A small test prompt: Start with plain text and a modest output limit. Add tools, images, or streaming only after a basic request succeeds.

Step-by-Step

1. Check the provider’s compatibility and documentation. Find the section for Open Responses or the exact API format your application expects. Verify the request path, authentication method, supported models, required fields, and whether streaming is available. Providers can implement only part of a format, so check support for any features you plan to use, such as tool calls or image input.
2. Set up credentials safely. Create or obtain an API key through the provider’s normal account or administrator process. Store it in a secret manager or environment variable, not in source code, a public repository, browser JavaScript, or logs. For example, a server-side application might read an environment variable named LLM_API_KEY. Use the exact authorization scheme documented by the provider; many use a bearer token, but do not assume that is universal.
3. Configure the endpoint and model. Use the provider’s documented base URL and response-creation route. Set the model to an identifier that provider actually offers. Avoid copying a URL, model name, or parameter list from a different service: similar APIs may use different routes or have different feature support.
4. Build a minimal request. Send an HTTP POST to the response endpoint with a JSON content type, the required authorization header, and a JSON body. A typical request includes a model and input, but the precise field names and accepted input shapes must match the provider’s documentation. For example, the body may conceptually contain a model identifier and a plain-text user prompt. Keep the first test simple; omit optional settings until you have confirmed their names and meanings.
5. Send the request and inspect the HTTP result. Use your client’s HTTP library or a command-line request tool. Check the status code and response body, not just whether the call returned. A successful status means the server accepted the request; it does not guarantee that your application extracted the generated text correctly.
6. Parse the response according to the format. Read the returned JSON structure and locate the output items or content parts defined by the format. Do not assume the answer is always at a fixed path such as choices[0].message.content; that shape belongs to other API conventions. Account for multiple output items, non-text content, and incomplete or refused responses where the format or provider exposes them.
7. Add streaming only if you need it. If supported, enable the documented streaming mode and process each event as it arrives. Streaming responses are not necessarily one complete JSON document: they may use server-sent events or another event protocol. Handle event boundaries, partial text, completion events, and connection closure. Keep a non-streaming path for simpler debugging.
8. Test errors and production behavior. Try an invalid model or a deliberately small output limit in a safe development environment to understand error handling. Add timeouts, limited retries for transient failures, and clear logging that excludes credentials and sensitive prompt content. Respect provider rate limits and usage limits, and avoid retrying permanent errors such as invalid credentials without correcting the configuration.

Common Mistakes

• Mixing API formats: Sending a request body for one API while calling another format’s route often produces validation errors. Use one documented schema end to end.
• Guessing fields: A field that looks familiar may be unsupported or named differently. Copy the provider’s current example, then change only the model and prompt for your first test.
• Assuming text is a single string: Responses may contain several items or content parts. Parse the documented structure rather than concatenating arbitrary fields.
• Putting a secret in a client app: Keys shipped in a web page or mobile binary can be extracted. Make provider calls from a protected server, or use the provider’s documented safe client flow if one exists.
• Retrying every failure: Retries can multiply load and cost. Retry only appropriate transient failures, use backoff, and stop when the provider reports a permanent request or authentication problem.

Tips

• Keep the base URL, model, and API key configurable so you can change providers without rewriting request logic.
• Validate configuration at startup and report missing settings without printing secret values.
• Write a small adapter around the provider-specific request and response details. Keep the rest of your application focused on your own internal message model.
• Set reasonable output limits and timeouts, and check how the provider handles cancellation and usage reporting.
• Use test prompts with predictable, non-sensitive content. Record status codes and request IDs when available, while following your data-handling requirements.

Troubleshooting

Authentication fails: Confirm that the key is present in the running process, has not expired or been revoked, and is sent in the documented header format. Check for whitespace or accidental quoting in environment-variable values. Never paste the key into a support post or diagnostic log.

The server reports a missing route or unsupported method: Recheck the base URL and response route in the provider’s documentation. Some gateways expose a compatible format under a different path, and a provider’s general API URL may not be the right endpoint.

The request is rejected: Read the error body for the field or value that failed validation. Check JSON syntax, required fields, model availability, and supported input types. Remove optional fields and retest with a minimal text request.

The request succeeds but no answer appears: Inspect the complete response, including item types and status or completion fields. Your code may be looking for a text field used by a different API. Add handling for non-text output or provider-specific incomplete states.

Streaming stalls or returns fragments: Confirm that streaming is enabled using the documented option and that your HTTP client handles the provider’s event format. Buffer partial data as required, process completion events, and test the same prompt without streaming to isolate the issue.

Calls time out or return rate-limit errors: Check provider status, configured timeouts, account limits, and request volume. Reduce concurrency if needed, use backoff for temporary throttling, and avoid repeating a request indefinitely.

Frequently Asked Questions

Is Open Responses a model?
No. It is an API format for interacting with a model. You still need a provider and a model that the provider makes available through that format.

Can I use any LLM provider?
Only if it supports the format directly or through a compatible gateway. Confirm route, authentication, schema, and feature support with that provider.

Do I need an SDK?
No. You can make HTTP requests directly. An SDK can simplify requests, but verify that it supports the exact format and provider endpoint you intend to use.

Does a successful response always contain plain text?
Not necessarily. Responses can include structured or non-text content, multiple items, or status information. Parse the documented response rather than assuming one text field.

Can I use streaming?
Yes, when both the provider and your client support it. Follow the provider’s event protocol and handle partial output, completion, and interrupted connections.

What should I do if the provider supports only some features?
Keep requests within the documented subset, or use a compatible gateway that supports the features you need. Test each required capability before relying on it in production.

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