[bob1029]

OpenAI has been nudging their users toward the Responses API lately. Chat completion can still do everything if you are clever. The obvious reason to push everyone into the Responses API is that the reasoning process can be locked down and encrypted. The semantics of the chat completion API are fundamentally transparent. 100% of the tokens are visible.

If you have patience and the willingness to endure a little bit of pain, you can still retain autonomy over the entire reasoning process while using the latest 5.6 model family. The only downside is that you are now fully responsible for it.

Consider that when you flip your agent's reasoning level to "xhigh" or whatever, it's not some magical model internals being pushed around. There isn't an actual "try harder" knob on the black box. This is merely orchestration of many instances of one or more model types based upon some proprietary harness logic. The chances you can develop a domain specific reasoning process that outperforms the frontier providers is still very good.

[dannyw]

You don't see real reasoning tokens with the Chat Completions API; and 'store: false' with Responses really isn't that different to Completions.

FWIW, if you have some tokens to spend, you might want to test Responses vs Completions in intelligence. Since GPT-5 models, we've consistently seen small, but statistically significant and reproducible improvements in intelligence with Responses API vs Completions.

However it works underneath the hood, it's real.

[bob1029]

> You don't see real reasoning tokens with the Chat Completions API

That's because there are no "reasoning" tokens. That is the entire point of doing it this way.

One major advantage is that I can switch to a different provider if OAI starts to get weird about this stuff and be able to have a fighting chance of re-adapting my harness to the new vendor's model. If 100% of my reasoning process is outsourced into the proprietary blackbox, there is little hope by comparison.

[hobofan]

> Chat completion can still do everything if you are clever.

On a purely functional level, yes. However for interactive use cases, the Completions API, as provided by OpenAI or Azure, if paired with reasoning effort of any kind, provides an awful user experience, as you will have a perceived delay of 10+ seconds until the first tokens stream in.

If using other providers that are exposing their thinking traces, this is less of an issue, as they've just extended the Comletions API format to have delta events with reasoning_content.

[apitman]

Can you give some more details on the technical differences between completions and responses that people actually care about? I found this information surprisingly hard to drum up.

[charcircuit]

OpenAI has hidden its reasoning for almost 2 years.

[trollbridge]

For codex specifically, it seems to have become much worse as of a few weeks ago.