Hi, 
Try this code:from odoo import fields, models, api

class YourModel(models.Model):
    _name = 'your.model'

    x_studio_float_field_3vq_1hkehadjt = fields.Float(compute='_compute_total_cost', store=True)

    @api.depends('order_line.x_studio_cot_total')
    def _compute_total_cost(self):
        for record in self:
            record.x_studio_float_field_3vq_1hkehadjt = sum(line.x_studio_cot_total for line in record.order_line)

Hope it helps