Cal. Lab. Code § 3755
If the employer is insured against liability for compensation, and if after the suffering of any injury the insurer causes to be served upon any compensation claimant a notice that it has assumed and agreed to pay any compensation to the claimant for which the employer is liable, such employer shall be relieved from liability for compensation to such claimant upon the filing of a copy of such notice with the appeals board. The insurer shall, without further notice, be substituted in place of the employer in any proceeding theretofore or thereafter instituted by such claimant to recover such compensation, and the employer shall be dismissed therefrom.
Such proceedings shall not abate on account of such substitution but shall be continued against such insurer.
Ca. Lab. Code § 3755