Six Copilot Models Retired Today: The Official Migration Map and What to Check Now

GitHub deprecated six AI models across all GitHub Copilot experiences on October 19, 2026, including Copilot Chat, inline edits, ask and agent modes, and code completions. The retired models are GPT-5.5, GPT-5.4, GPT-5.4 mini, GPT-5 mini, Gemini 3.7 Flash, and Grok 4.5, and GitHub's changelog explicitly asked developers to update their workflows and integrations to supported models before the date. Most developers will barely notice the swap, but teams running custom integrations, strict compliance policies, or workflows tuned to a specific retired model's quirks face real breakage risk.

GitHub Copilot Retires Six Models: What You Need to Know

The deprecation was announced in advance: GitHub's changelog, published September 18, 2026, listed all six models with a single retirement date and a suggested alternative for each. The move consolidates Copilot's roster around the GPT-5.6 family, which GitHub introduced in July 2026 in three variants — Sol, Terra, and Luna — alongside updated Gemini and Grok options.

Reporting on the retirement by Marcus Bell at Shattered frames the stakes plainly: GitHub's bet is that most developers will barely notice, since GPT-5.6 Sol and Luna, plus Gemini 3.8 Flash, are newer and presumably more capable than what they replaced. The riskier bet, Bell writes, is on the minority running custom integrations or workflows tuned to a specific retired model's quirks.

One caveat applies throughout: GitHub has not published a detailed behavioral diff between the retired models and their replacements, so no one can yet quantify how output style or quality will shift. Teams relying on consistent output characteristics should not assume parity.

GitHub Copilot Model Migration Map

The table below organizes GitHub's official deprecation notice into a single reference, correlating each retired model with its designated successor and the successor's intended function where GitHub has documented one. The GPT-5.6 variant descriptions come from GitHub's July 2026 changelog entry introducing the family.

Official mapping of retired GitHub Copilot models to suggested alternatives
Retired Model	Deprecation Date	Suggested Alternative	Primary Use Case of New Model
Gemini 3.7 Flash	2026-10-19	Gemini 3.8 Flash	Not detailed in GitHub's documentation
GPT-5.5	2026-10-19	GPT-5.6 Sol	Highest reasoning ceiling in the family; best for complex reasoning over large codebases and demanding, long-running agentic work
GPT-5.4	2026-10-19	GPT-5.6 Sol	Highest reasoning ceiling in the family; best for complex reasoning over large codebases and demanding, long-running agentic work
GPT-5.4 mini	2026-10-19	GPT-5.6 Luna	Lightweight, cost-efficient variant for smaller, faster tasks; lowest-cost option in the family
GPT-5 mini	2026-10-19	GPT-5.6 Luna	Lightweight, cost-efficient variant for smaller, faster tasks; lowest-cost option in the family
Grok 4.5	2026-10-19	Grok 4.6	Not detailed in GitHub's documentation

With this mapping, a developer can identify the correct replacement for their workflow without cross-referencing multiple announcements. Note that GPT-5.6 Terra, the balanced default for everyday interactive and agentic coding, is available in Copilot but does not appear in the official replacement list — it may suit interactive use cases even though GitHub's deprecation notice names Sol and Luna as the suggested alternatives.