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OpenAI Chat Completions: Production-Ready Guide

गाइड · EN · 2026-09-24

What the Chat Completions Format Solves

The OpenAI-compatible chat completions format is a standard HTTP interface for sending a conversation to an AI model and receiving its next response. Its main endpoint is usually POST /v1/chat/completions. Because the shape is widely adopted, you can often keep your existing OpenAI SDK, agent framework, Claude Code, or Codex integration and change only the API base URL, API key, and model name.

For a cost-conscious production setup, 59API provides an OpenAI-compatible relay at https://api.59api.com. It offers pay-as-you-go access to native official-quality Claude and GPT models, including Claude Opus, Sonnet, Haiku, and Fable options, without requiring you to rewrite an OpenAI-style client. Check the provider dashboard for the exact model identifiers available to your account before deploying.

Build Your First Request

A minimal request has two required fields: model, which selects the model, and messages, an ordered array representing the conversation. Send an Authorization header in the form Bearer YOUR_API_KEY and Content-Type: application/json. With 59API, configure your client base URL as https://api.59api.com/v1, then call the chat completions resource normally.

Conceptually, the request body looks like this: {"model":"your-model-id","messages":[{"role":"system","content":"You are a concise support assistant."},{"role":"user","content":"How do I reset my password?"}]}. The model reads messages in order and generates the next assistant message.

Do not rely on the server to remember previous requests. For each follow-up, send the relevant prior messages again. In production, retain a short recent history, summarize older turns, and remove secrets or unnecessary personal data before sending them to any model.

Control Output Without Overcomplicating Prompts

Common optional parameters include temperature, max_tokens or provider-supported completion-token limits, top_p, stop, and stream. Use a low temperature for extraction, support workflows, and deterministic formatting; use a higher value when brainstorming. Set a completion limit to control both latency and spend. For structured workflows, explicitly describe the desired fields and validate the returned result in your application instead of trusting text blindly.

A normal response contains an id, model metadata, usage information, and a choices array. For standard text replies, read choices[0].message.content. Also record usage values when available: prompt tokens show input size, completion tokens show generated size, and total tokens help explain costs and unusually large requests.

Add Streaming for a Better User Experience

Set stream to true when your interface should display text as it is generated. Instead of one complete JSON response, the server sends Server-Sent Events containing small delta objects. Append each non-empty choices[0].delta.content value to the visible answer. When the stream ends, finalize the message and save it to your conversation history.

Your stream handler should tolerate partial chunks, empty deltas, connection interruptions, and a final completion marker. Never assume that one chunk equals one word or one sentence. On an interrupted stream, show a recoverable status, preserve received text, and offer a retry rather than silently discarding the response.

Use Tools When the Model Must Take Action

Chat completions can also declare tools, typically function definitions with a name, description, and JSON-schema-like parameters. For example, a delivery assistant may expose get_order_status with an order_id parameter. If the model returns a tool call, your application—not the model—must validate arguments, enforce authorization, call the trusted backend, and send the tool result back as a new conversation message.

Treat tool arguments as untrusted input. Apply schema validation, allowlists, rate limits, and idempotency protection for actions such as refunds, emails, or database changes. This separation is what turns a helpful prototype into a safe production agent.

Production Checklist and Low-Cost Deployment

59API is a practical choice when you want this familiar format with low pay-as-you-go costs, native official-quality model access, and compatibility across OpenAI SDK-based tools. Its referral rebate can further reduce ongoing development costs. When you are ready to test your first request, sign up for 59API, create an API key, and point your existing compatible client at its base URL.

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