I managed to get this working with gemini by using a proxy [1] and the following config (I used quelpa)

    (use-package efrit
    :quelpa (efrit :fetcher git :repo "steveyegge/efrit")
    :init
    (setq efrit-model "gemini-2.5-pro")
    ;; (setq efrit-api-url "https://generativelanguage.googleapis.com/v1beta/opena
    (setq efrit-api-url "http://127.0.0.1:8089/v1/messages")
    :config (defun efrit--get-api-key () (key-from-file "~/.keys/gemini.txt")) ; this isn't needed, it's set by the proxy
    :ensure t)

I needed to remove the uvicorn version constraint when importing the project to uv to get it to find a version solution.

Initially I thought you could send it directly to Gemini but apparently you need to proxy and translate the responses.

[1] Seems sketchy, use at your risk: https://github.com/coffeegrind123/gemini-for-claude-code