A bit late, but we can make an educated guess based on the announcement. If GPT-5.3-Codex is now part of the unified 5.4 model, I would not expect a separate 5.4-Codex release. It seems more likely that the next Codex-style update would appear as part of a future version such as 5.5. That said, this is only speculation about what might come next.
GPT‑5.4 brings together the best of our recent advances in reasoning, coding, and agentic workflows into a single frontier model. It incorporates the industry-leading coding capabilities of GPT‑5.3‑Codex while improving how the model works across tools, software environments, and professional tasks involving spreadsheets, presentations, and documents.