GitHub Copilot Is Deprecating Six More Models on October 19 — and the Replacements Name GPT-5.6

GitHub is pruning its Copilot model lineup again. A changelog entry published September 18 announces that six models will be deprecated across all GitHub Copilot experiences — Chat, inline edits, ask and agent modes, and code completions — on October 19, 2026.

The models on the chopping block, with GitHub’s suggested alternatives:

Gemini 3.7 Flash → Gemini 3.8 Flash. GPT-5.5 → GPT-5.6 Sol. GPT-5.4 → GPT-5.6 Sol. GPT-5.4 mini → GPT-5.6 Luna. GPT-5 mini → GPT-5.6 Luna. Grok 4.5 → Grok 4.6.

This is a separate announcement from the October 2 retirements GitHub flagged earlier in September (Gemini 3.5 and 3.6 Flash, Kimi K2.7 Code, and Claude Opus 4.7). The cadence is becoming a pattern: GitHub announces model removals roughly a month out, keeps the deprecated names working until the cutoff, and steers users to the replacements.

The churn is the business model

Two deprecation announcements inside two weeks is aggressive even by 2026 standards, and it reflects how Copilot’s positioning has changed. With GitHub serving a broad multi-model catalog — OpenAI, Anthropic, Google, xAI, and others — keeping older generations live costs context window overhead, evaluation time, and user confusion, while the frontier keeps moving underneath them. The company has settled on a steady pruning rhythm: announce with roughly a month of lead time, keep the old models working through the transition, and make the default-migration path automatic for everyone who hasn’t opted out of defaults.

The interesting column is the alternatives

Deprecations are routine; the suggested alternatives are where the news is. The changelog names GPT-5.6 Sol and GPT-5.6 Luna as the successors to the GPT-5.x family in Copilot, and Grok 4.6 as the replacement for Grok 4.5. These names surface here as Copilot’s recommended migration targets — effectively confirming the next OpenAI and xAI model generations are already slotted into GitHub’s roadmap, even if neither lab has said much about them publicly.

For Copilot Enterprise and Business customers, the migration is mostly automatic: under default model enablement, the suggested alternatives are enabled unless an administrator has turned off the global default or explicitly disabled the model. Admins who did either of those things will need to enable the replacements through their model policies in Copilot settings. GitHub notes that no action is required to remove the deprecated models after October 19 — they simply stop being served.

The practical advice is the same as every Copilot deprecation cycle: if your workflows, custom agents, or model policies pin any of the six outgoing models by name, update them before October 19. If you rely on defaults, GitHub handles the swap. And if you’re watching the model race, the changelog just told you what the next round of names will be.