GitHub announced on September 18, 2026 that six models will be deprecated in GitHub Copilot on October 19, 2026. Its official notice covers Copilot Chat, inline edits, ask and agent modes, and code completions.
This is a separate deadline from the October 2 retirement wave previously reported by QATechTools.
Which models are affected?
| Retiring October 19 | GitHub suggested alternative |
|---|---|
| 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 |
For Copilot Business and Enterprise, suggested replacements are automatically enabled under default model enablement unless an administrator has disabled the global default or the individual model. If the global default is off, administrators can enable replacements through model policies. Enabled models appear in the selector in supported experiences; GitHub says no action is required to remove retired models.
Why this matters for QA engineers
A change of model can change the assertions, test data and patches generated from the same request. Our QA recommendation is to treat the October 19 switch as a dependency change: compare outcomes before adopting a new baseline. The announcement does not establish equivalent test-generation accuracy or promise better defect detection.
What to check before October 19
Confirm access: have a representative managed user select the intended replacement in each Copilot client your team uses. Record policy restrictions before the deadline.
Compare real QA tasks: replay a small fixed set of test-generation, failure-triage and repair requests. Run the resulting tests and inspect whether assertions detect the intended defect; fluent explanations alone are insufficient evidence.
Update team references: replace retired model names in runbooks and evaluation records. Keep the model, client version and observed results together so later regressions are traceable.
Source verified September 20, 2026. Retirement dates and replacement mappings come from GitHub; QA checks above are QATechTools editorial recommendations.