# Objective
 
Fixes auto-compaction for ChatGPT Subscription / Codex-backed GPT models
by treating the Codex `context_window` as the usable context budget
instead of reserving an inferred `128k` output budget.
 
- Fixes #59555 

## Solution

Zed previously reported `max_output_tokens = 128_000` for
`openai_subscribed` models. Generic agent code subtracts
`max_output_tokens` from `max_token_count` when computing the effective
input budget, so `openai_subscribed` models ended up with:

- `max_token_count = 272_000`
- `max_output_tokens = 128_000`
- effective compaction budget = `144_000`
- default `90%` threshold = `129_600`

## Testing

Tested with a heavy prompt to confirm that the auto compaction is indeed
now triggered at 90% (default)

<img width="385" height="183" alt="image"
src="https://github.com/user-attachments/assets/da569152-f687-4366-868a-a6559b948ce5"
/>

This made Zed compact around the halfway point of the actual Codex
context window.

Codex model metadata exposes `context_window = 272000` and does not
expose a `max_output_tokens` cap. Codex also compacts against the
context window directly, rather than subtracting an output reservation.
The subscribed backend also rejects the `max_output_tokens` request
parameter, so Zed already omits it when serializing requests.

This change makes `openai_subscribed` report no known max output token
cap, which matches also that split token display is disabled for these
models.


## Self-Review Checklist:

- [X] I've reviewed my own diff for quality, security, and reliability
- [X] Unsafe blocks (if any) have justifying comments
- [X] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [X] Tests cover the new/changed behavior
- [X] Performance impact has been considered and is acceptable

---

Release Notes:

- agent: Fix compaction happening too early when using the ChatGPT
subscription provider.