feat(models): add github_copilot/gpt-5.3-codex and github_copilot/claude-opus-4.6-fast

[Chesars]

Relevant issues

Fixes #21148

Pre-Submission checklist

• I have Added testing — JSON-only change to model registry, no code logic changed
• My PR passes all unit tests — no code changes to test
• My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🆕 New Feature

Changes

Add two missing GitHub Copilot models to model_prices_and_context_window.json:

• github_copilot/claude-opus-4.6-fast — chat mode, 128k input / 16k output
• github_copilot/gpt-5.3-codex — responses mode, 128k in/out

Both follow the existing github_copilot model pattern.

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Project	Deployment	Actions	Updated (UTC)
litellm	Ready	Preview, Comment	Feb 16, 2026 3:26pm

[greptile-apps]

Greptile Summary

Adds two new GitHub Copilot model entries to the model registry: github_copilot/claude-opus-4.6-fast (chat mode, 128k input / 16k output) and github_copilot/gpt-5.3-codex (responses mode, 128k input / 128k output).

• Both entries follow the established github_copilot model pattern exactly, matching the structure of analogous existing models (claude-opus-4.5 and gpt-5.1-codex-max respectively)
• Entries are inserted in alphabetical order within the JSON file
• Both the primary and backup JSON files are updated identically
• No code logic changes — JSON-only model registry additions

Confidence Score: 5/5

• This PR is safe to merge — it only adds two new model entries to a JSON registry with no code logic changes.
• The PR adds two well-structured JSON entries that exactly follow existing patterns for github_copilot models. Both files are updated consistently. No code changes, no risk of runtime errors, and no security implications.
• No files require special attention.

Important Files Changed

Filename	Overview
model_prices_and_context_window.json	Adds two new github_copilot model entries (claude-opus-4.6-fast and gpt-5.3-codex) following existing patterns exactly. JSON structure is valid, entries are alphabetically ordered, and both models mirror existing analogous entries.
litellm/model_prices_and_context_window_backup.json	Backup file mirrors the primary model prices JSON exactly, with identical additions of the two new github_copilot model entries.

Flowchart

flowchart TD
    A[model_prices_and_context_window.json] --> B[github_copilot/claude-opus-4.6-fast]
    A --> C[github_copilot/gpt-5.3-codex]
    B --> D[mode: chat]
    B --> E[128k input / 16k output]
    B --> F[endpoint: /v1/chat/completions]
    C --> G[mode: responses]
    C --> H[128k input / 128k output]
    C --> I[endpoint: /v1/responses]
    A --> J[litellm/model_prices_and_context_window_backup.json]
    J --> K[Identical copy]

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