---
title: "index 60"
description: "import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem';"
type: skill
canonical_url: https://claudary.paisolsolutions.com/skills/index-60
source: "Claudary"
difficulty: intermediate
author: "Claude Code Knowledge Pack"
date: 2026-07-10T11:25:31.017Z
license: CC-BY-4.0
attribution: "index 60 — Claudary (https://claudary.paisolsolutions.com/skills/index-60)"
---

# index 60
import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem';

## Overview

---
slug: gpt_5_3_codex
title: "Day 0 Support: GPT-5.3-Codex"
date: 2026-02-24T10:00:00
authors:
  - sameer
  - krrish
  - ishaan-alt
description: "Day 0 support for GPT-5.3-Codex on LiteLLM, including phase parameter handling for Responses API."
tags: [openai, gpt-5.3-codex, codex, day 0 support]
hide_table_of_contents: false
---

import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';

LiteLLM now supports GPT-5.3-Codex on Day 0, including support for the new assistant `phase` metadata on Responses API output items.

{/* truncate */}

## Why `phase` matters for GPT-5.3-Codex

`phase` appears on assistant output items and helps distinguish preamble/commentary turns from final closeout responses.

Reference: [Phase parameter docs](https://developers.openai.com/api/reference/overview)

Supported values:
- `null`
- `"commentary"`
- `"final_answer"`

Important:
- Persist assistant output items with `phase` exactly as returned.
- Send those assistant items back on the next turn.
- Do **not** add `phase` to user messages.

## Docker Image

```bash
docker pull ghcr.io/berriai/litellm:v1.81.12-stable.gpt-5.3
```

## Usage 

<Tabs>
<TabItem value="proxy" label="LiteLLM Proxy">

**1. Setup config.yaml**

```yaml
model_list:
  - model_name: gpt-5.3-codex
    litellm_params:
      model: openai/gpt-5.3-codex
```

**2. Start the proxy**

```bash
docker run -d \\
  -p 4000:4000 \\
  -e ANTHROPIC_API_KEY=$OPENAI_API_KEY \\
  -v $(pwd)/config.yaml:/app/config.yaml \\
  ghcr.io/berriai/litellm:v1.81.12-stable.gpt-5.3 \\
  --config /app/config.yaml
```


**3. Test it**

```bash
curl -X POST "http://0.0.0.0:4000/v1/responses" \\
  -H "Content-Type: application/json" \\
  -H "Authorization: Bearer $LITELLM_KEY" \\
  -d '{
    "model": "gpt-5.3-codex",
    "input": "Write a Python script that checks if a number is prime."
  }'
```

</TabItem>
</Tabs>

## Python Example: Persist `phase` with OpenAI Client + LiteLLM Base URL

```python
from openai import OpenAI

client = OpenAI(
    base_url="http://0.0.0.0:4000/v1",  # LiteLLM Proxy
    api_key="your-litellm-api-key",
)

items = []  # Persist this per conversation/thread


def _item_get(item, key, default=None):
    if isinstance(item, dict):
        return item.get(key, default)
    return getattr(item, key, default)


def run_turn(user_text: str):
    global items

    # User message: no phase field
    items.append(
        {
            "type": "message",
            "role": "user",
            "content": [{"type": "input_text", "text": user_text}],
        }
    )

    resp = client.responses.create(
        model="gpt-5.3-codex",
        input=items,
    )

    # Persist assistant output items verbatim, including phase
    for out_item in (resp.output or []):
        items.append(out_item)

    # Optional: inspect latest phase for UI/telemetry routing
    latest_phase = None
    for out_item in reversed(resp.output or []):
        if _item_get(out_item, "type") == "output_item.done" and _item_get(out_item, "phase") is not None:
            latest_phase = _item_get(out_item, "phase")
            break

    return resp, latest_phase
```

## Notes

- Use `/v1/responses` for GPT Codex models.
- Preserve full assistant output history for best multi-turn behavior.
- If `phase` metadata is dropped during history reconstruction, output quality can degrade on long-running tasks.

---

Source: [Claudary](https://claudary.paisolsolutions.com/skills/index-60) · https://claudary.paisolsolutions.com