October 2026 was a heavy shipping month for OpenAI, and most of it happened quietly in release notes rather than on a stage. Coming off DevDay 2026 on September 29 — which the company billed as its biggest event yet, with more than twenty announcements across ChatGPT, Codex and its model lineup — the last four weeks brought security features, an advertising push, a new generally available API, and two model-lineup changes that affect which model you get by default.

Everything below is drawn from OpenAI's official ChatGPT release notes and product announcements, with the date each change landed.

Locked chats arrive for ChatGPT Business (October 20)

The most security-relevant change of the month: locked chats began rolling out on October 20 for ChatGPT Business, with availability appearing gradually across the web app, iOS, Android, and the macOS and Windows desktop apps. Locked conversations are protected separately from your regular chat history — a direct answer to the very common workplace pattern of pasting client data, contracts, or internal notes into a chat that anyone with device access could otherwise open.

Rollout is gradual, so Business workspace admins may see the control appear at different times across their teams. If your organization handles sensitive material, this is the feature to turn on first.

Richer answers, and ads in 26 more countries (October 21)

Two user-facing changes landed the following day. First, ChatGPT can now combine text, visuals, and interactive elements inside a single answer — a step past the plain markdown response model toward answers that behave more like small applications. Second, ChatGPT Ads expanded to 26 new countries on October 21, continuing the monetization push that started earlier in the year. Free and Plus users in those markets will start seeing sponsored results inside some conversations; Business and Enterprise workspaces are not the target of the ad expansion.

The Decisions API goes generally available (October 22)

For developers, the headline is that the Decisions API — running on GPT-6 Luna — reached general availability on October 22, with expanded per-request capabilities. General availability matters more than the announcement itself: it means OpenAI is putting production support, stability commitments, and billing behind the endpoint. Teams that were evaluating it during preview can now build on it without expecting breaking changes. If you missed the preview period, the Decisions API is OpenAI's structured-decision endpoint — it returns a justified choice between options rather than free-form text, which is the shape you want for approval workflows, routing, and policy checks.

The model lineup: Sol rises, GPT-5.5 retires

Two model changes rounded out the month:

  • GPT-6.1 Sol was introduced as a new tier in the GPT-6 family, positioned at near-Astra performance at lower cost, and is now available for complex work in ChatGPT and Codex.
  • GPT-5.5 was retired on October 14 — removed from ChatGPT, ChatGPT Work, and Codex on all plans. Notably, the OpenAI API is not affected, so production applications calling GPT-5.5 over the API keep working for now; consumer surfaces do not.

The retirement is the part most teams feel. If your workspace prompts were tuned around GPT-5.5's habits, your default outputs changed overnight. The practical move is to re-run your ten most important saved prompts against Sol and compare before you need them.

What this means for different users

Business admins: enable locked chats as the rollout reaches your workspace, and review the ads settings if any of your markets are in the expansion list. Developers: the Decisions API is now a stable build target; GPT-5.5 API access continues, but the consumer retirement is a signal — start your migration testing now. Everyday users: expect richer, mixed-media answers and, in ad-supported markets, sponsored results in some conversations.

Frequently asked questions

Do locked chats exist on free or Plus plans?

No — the October 20 release notes list locked chats for ChatGPT Business, rolling out gradually across platforms.

Is GPT-5.5 gone from the API too?

No. The October 14 retirement removed it from ChatGPT, ChatGPT Work, and Codex on all plans; OpenAI's API was explicitly not affected.

What model is inside the Decisions API?

GPT-6 Luna, per the October 22 general-availability announcement.

Sources