Model picker simplified; Thinking Light removed

Updated model picker for ChatGPT Enterprise and Edu on web, iOS, and Android. New options include Instant, Medium, High, Extra High, Pro Standard, and Pro Extended. Medium replaces Thinking Standard, High replaces Thinking Extended, and Extra High replaces Thinking Heavy. Pro Standard and Pro Extended use GPT-5.5 Pro. Thinking Light is no longer available. All six options available to Enterprise and Edu workspaces subject to workspace access settings. Reasoning Model Access controls Medium, High, and Extra High. Pro Model Access controls Pro Standard and Pro Extended. On iOS and Android, picker appears at top of conversation; on web, in message composer.