Model APIs
Compare OpenAI Responses API and Chat Completions for new apps, agent workflows, tool use, conversation state, structured outputs, file search, web search, and migration planning.
Comparison
| Option | Best for | Strengths | Tradeoffs | Use when |
|---|---|---|---|---|
| Responses API | New apps, agentic workflows, typed items, built-in tools, file search, web search, and multimodal use | A newer unified API path with typed input and output items and better alignment with OpenAI's agent-building direction. | Existing chat code may need changes to message mapping, state management, logging, and tool handling. | You are building or refactoring a serious OpenAI integration today. |
| Chat Completions | Stable legacy chat apps, simple message generation, and code paths that do not need new tools | Familiar, widely used, and often enough for simple chat or generation flows. | Less aligned with newer Responses API features and agent primitives. | The app is stable, low-risk, and migration has not yet been prioritized. |
| Dual-path migration | Production systems that need side-by-side testing before switching traffic | Lets teams compare quality, latency, cost, state handling, and output contracts before cutover. | Requires extra logging, test harnesses, and a temporary compatibility layer. | The API powers revenue, customer support, or critical internal workflows. |
The migration is not only an endpoint name change. Chat Completions uses message arrays as the central mental model. Responses uses typed input and output items, which can include messages, reasoning, function calls, and tool outputs.
If the product uses file search, web search, remote MCP servers, function calling, or agent-like workflows, Responses is the cleaner long-term API path.
A safe migration compares the current production behavior against the new path on realistic prompts. The goal is not only to compile but to preserve or improve quality, latency, cost, and observability.
Decision Rules
Use Responses API for new OpenAI projects.
Keep Chat Completions temporarily for stable legacy apps without tool needs.
Move sooner when you need file search, web search, agents, multimodal, or richer output items.
Migrate behind evals, traces, and a rollback plan for production workflows.
Related Guides
Plan migration before the Assistants API sunset.
OpenUse schema-first responses after moving API paths.
OpenHandle the higher-risk migration away from Assistants API.
OpenCompare provider strategy after choosing the OpenAI API path.
OpenMake Responses output reliable for downstream code.
OpenChinese Archive
Topic Hubs
FAQ
Use Responses API for new OpenAI apps unless you have a specific legacy constraint. It is better aligned with tools, agents, typed items, and newer platform direction.
Simple text generation can be straightforward, but apps with tools, state, streaming, logging, or structured outputs need careful mapping and regression tests.
No. Conversation state still has cost and design implications. Use provider documentation and your own traces to understand billing, context, and truncation behavior.
Source Links
Reference
Official OpenAI migration guide from Chat Completions to Responses.
OpenReference
Official OpenAI documentation for managing conversation state.
OpenReference
Official OpenAI documentation for tools, web search, file search, MCP, and function calling.
OpenThe strongest decision is always local to your workflow. Save the vendor links, define a representative task, record the exact prompt or command, and compare the final evidence instead of the marketing claim.
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