The parties’ arbitration agreement constitutes a contract to refer disputes that have arisen or may arise in the future between them to arbitration. The freedom of parties to consensually execute an arbitration agreement is known as the principle of party autonomy. Fundamentally, party autonomy affects arbitral procedure and can influence, for example, the process of appointing a tribunal, the nature of the evidentiary hearing, the appointment of a tribunal secretary, and either party’s rights to seek interim relief from a supervisory or competent court. Naturally, there is a balance between party autonomy and the powers of the tribunal or the arbitral institution. Evolution in many arbitral rules has tended to increase power, both mandatory and discretionary, in favor of the tribunal such that party autonomy is directly contradicted and compromised. This is especially so when institutional rules seek to impose default rules which curtail parties’ legal rights and/or enforce “mandatory” rules. Examples include 2020 LCIA Rules, Article 18.3 (on changes to party representatives); 2021 ICC Rules, Article 12.9 (on tribunal appointment) and 2020 Draft AFSA Rules Article 20.1 (on tribunal control of proceedings after constitution regardless of party agreements) among others. In the absence of data from empirical research, the authors propose that arbitral innovation should not further erode the autonomy principle (leaving, at best, parties only open to amend default institutional rules post-tribunal constitution) and should make mandatory only those rules that are essential to render an enforceable award.