This epic is to capture work by the Custom Models and Duo Chat team to enable end-user model selection in the Gitlab UI for Agentic Chat. This epic builds off of [previous work](https://gitlab.com/groups/gitlab-org/-/epics/18818) to enable Model Selection controls for top-level administrators at: * Namespace-level admin on GitLab.com * Instance-level admins on Self-Managed and Dedicated accessing Duo features via the GitLab.com AIG/WFS **In Scope** This epic focuses on the first iteration and smallest scope to quickly enable end-user model selection for customers. As such, this epic will focus on: * GitLab.com end users * Agentic Chat in the existing GitLab UI * a limited scope of supported models - Claude 3.5 Sonnet, Claude 3.7 Sonnet, and Claude 4 Sonnet **Out of Scope** * end-user model selection for Agentic Chat in the IDE * support for Self-Managed and Dedicated customers using the GitLab.com AIG/WFS * model selection for Code Suggestions agents in the IDE * admin-defined allowable models * new UI side panel integration * additional model family support (i.e. OpenAI GPTs or Google Gemini) ### Definition of Done * If the namespace administrator has pinned a specific model for use with that namespace, there is no action or model choice for the end user within that namespace (pinned model is enforced) * end-user can see the chosen model set in the model drop down, but cannot change * If the namespace administrator had NOT pinned a specific model for use with that namespace, then the end-user can choose from among the available Gitlab AI Vendor models * for this first iteration, those models are restricted to Claude 3.5 Sonnet, Claude 3.7 Sonnet, and Claude 4 Sonnet * if the end-user changes their model choice, the conversation does not persist * user model preferences persist across browser sessions