OpenAI has updated ChatGPT with GPT-5.3 Instant Mini as the fallback model after users hit rate limits for GPT-5.3 Instant, while also introducing a new $100-a-month Pro plan that expands Codex usage for heavier users. The changes, announced in the April 9 release notes, show how OpenAI is packaging ChatGPT more tightly around both conversational use and developer workflows.