OpenAI upgrades GPT-5.5 Instant readability, retires o3 and GPT-4.5

OpenAI rolled out a GPT-5.5 Instant update aimed at more natural, easier-to-read responses with fewer long bullet lists, while removing the Canvas side panel from both Instant and Thinking variants. Writing and coding tasks now happen inline through special blocks. The company is retiring legacy models too: GPT-4.5 leaves ChatGPT on June 27 after a 30-day sunset and o3 follows on August 26 after 90 days. o3 stays in the API for now while GPT-4.5 was already pulled there earlier.

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