How do I choose the mode/backend?

[oatmealm]

Does evedel only uses whatever is defined in gptel-model as the default? Can I set it directly or need to define as a buffer local value?

[daedsidog]

Right now, Evedel uses only gptel-request, so you do it in the same manner you do it in gptel, by binding gptel-model and gptel-backend.

Can I set it directly or need to define as a buffer local value?

Yes, same way as you would for other gptel commands.

You can read more about it by consulting the documentation of gptel-request.