I tried this but it not active :
class ResPartner(models.Model):
    _inherit = 'res.partner'
    type_customer = fields.Char('Type customer', default='Normal')
    @api.depends('total_invoiced')
    def _compute_type_customer(self):
        for rec in self:
            if rec.total_invoiced > 1000:
                rec.type_customer = 'Gold'
            else:
                rec.type_customer = 'Normal'

Hi,

You can use compute function which depends 'total_invoiced' to calculate value on new field.

@api.depends('total_invoiced')
def _compute_type_customer(self):
    for rec in self:
        if rec.total_invoiced > 1000:
            rec.type_customer = 'Gold'
        else:
            rec.type_customer = ''

Hope it helps