I have a feeling that the chatgpt ui does some behind-the scenes tuning as well--hidden prompt engineering if you will. I migrated to the api and 4o still seems different. Most obvious, I don't get the acks that make me feel like I should run for president.

Even ChatGPT 5 confirmed this,

why does the gpt-4o api not do this?

ChatGPT said:

Because the GPT-4o API is tuned and delivered in a neutral, low-intrusion style by default.

When OpenAI built GPT-4o for API use, they optimized it for:

    Predictable formatting (so it works well in code, pipelines, chatbots, etc.)

    Minimal unsolicited chatter (no “Nice!” or “Great job!” unless explicitly prompted)

    Deterministic tone — so that two API calls with the same input produce consistent, professional output without extra filler.

In API mode, you’re the one defining the personality, so if you want that “Good! Looks like you’re digging in” style, you have to bake it into the system prompt, for example:

The GPT-4o you talk to through ChatGPT and the GPT-4o you access via the API are different models... but they're actually both available via the API.

https://platform.openai.com/docs/models/gpt-4o is gpt-4o in the API, also available as three date-stamped snapshots: gpt-4o-2024-11-20 and gpt-4o-2024-08-06 and gpt-4o-2024-05-13 - priced at $2.50/million input and $10.00/million output.

https://platform.openai.com/docs/models/chatgpt-4o-latest is chatgpt-4o-latest in the API. This is the model used by ChatGPT 4o, and it doesn't provide date-stamped snapshots: the model is updated on a regular basis without warning. It costs $5/million input and $15/million output.

If you use the same system prompt as ChatGPT (from one of the system prompt leaks) with that chatgpt-4o-latest alias you should theoretically get the same experience.

But it always gives answers like that for questions where it doesn't know the actual reason.

> Even ChatGPT 5 confirmed this,

>> why does the gpt-4o api not do this?

> ChatGPT said:

>> Because the GPT-4o API is tuned and delivered in a neutral, low-intrusion style by default.

But how sure are you that GPT-5 even had this data, and if it has it, it's accurate? This isn't information OpenAI has publicly divulged and it's ingested from scraped data, so either OpenAI told it what to say in this case, or it's making it up.