Not possible to select reasoning mode for GPT-5.4 in URL queries

TLDR: When using /new url with params model=gpt-5.4-reasoning or model=gpt-5.4-instant the suffix is not respected and whatever mode you last selected in the UI gets used.

I use Kagi bangs to quickly open T3 chats.

I am hoping to have 2 bangs:

• t3: 5.4 in instant mode

• t3r: 5.4 in reasoning mode at medium settings

I have discovered that even though t3 chat unified 5.4 reasoning/instant under one model in UI, unlike 5.3. When creating chats through URL query parameters it still expect one of gpt-5.4-reasoning or gpt-5.4-instant.

Excerpt from error text when making a url with a bogus model name (I tried gpt-5.4 initially):
```json

{

"path": [

"model"

],

"message": "Expected \"gpt-5.4-instant\", actual \"gpt-5.4\""

},

{

"path": [

"model"

],

"message": "Expected \"gpt-5.4-reasoning\", actual \"gpt-5.4\""

},
```

However, in my testing the suffix is not respected and whatever I used last on t3 chat is what gets picked.

For example:

• create a new chat, pick gpt-5.4 and set it to reasoning-medium

• open a new tab with url
  https://t3.chat/new?model=gpt-5.4-instant&q=hello

• Observe the settings are set to reasoning-medium

• Expected: should be instant

Inverse:

• In a chat with 5.4, pick instant

• open a new tab with url
  https://t3.chat/new?model=gpt-5.4-reasoning&q=hello

• Observe the settings are set to instant

• Expected: should be some form of reasoning (I didn’t specify medium, so any level would be fine here, just not instant)

I have not yet tried to explicitly specify the reasoning level with an extra param since I don’t know if such a param exists, I will test that next, but I think the suffixes should be respected regardless of if one can control reasoning effort with a separate parameter?