GitHub has set 16 November 2026 as the retirement date for three models in Copilot: Claude Opus 4.8, Claude Opus 5 and GPT-5.6 Terra. If you have a workflow, an agent config or a pinned model setting referencing any of them, it stops working that day.
Opus 4.8 gets a partial reprieve: it remains available to individual annual-plan subscribers. Everyone else, including organisations, loses all three. GitHub's suggested replacements are Claude Opus 5.5 for the Opus models, and GPT-6.1 Sol or GPT-6 Luna for Terra.
The detail worth knowing is that this is a Copilot decision, not a model deprecation. Claude Opus 5 remains available through Anthropic's own API well beyond this date — so if you have pipelines depending on that specific model, the fix may be moving the call rather than changing the model.
What to do before 16 November
Search your repositories for pinned model names in Copilot configuration, agent definitions and any CI steps that specify a model. A pinned name that silently falls back to a default is the failure mode that costs you a week of confusing output rather than a clean error.
Sources:
GitHub Changelog