Recently, I wrote here about the AI Smackdown presented at a Feb. 8 meeting of the Southern California Association of Law Libraries, where a panel of three law librarians reported on their comparison of the AI answers delivered by three leading platforms – Lexis+AI, Westlaw Precision AI, and vLex’s Vincent AI.

Having been playing around of late with Deep Research, the AI agent from OpenAI that is capable of completing multi-step research tasks and synthesizing large amounts of online information, I wondered how much of a contender it could be against those legal research prizefighters. 

[My other Deep Research posts: What Is OpenAI’s Powerful New Deep Research Tool Capable Of? I Use It to Analyze the Legality of President Trump’s Pause of Federal Grants; Today’s Experiment with OpenAI’s Deep Research: Picking the Best Cloud-Based Law Practice Management Software for a Small Law Firm; A Compendium of Legal Ethics Opinions on Gen AI (As Compiled by – You Guessed It – Gen AI).]

To test it, I decided to start with just one of the three questions the law librarians used in their smackdown. Of the three questions they threw into the ring, one turned out to be particularly tricky and elicited much-different answers from each of the commercial legal research platforms. That question was:

“What is the standard for appealing class certification? (California)”

What made it tricky was something called the “death knell” doctrine, which requires that denials of class actions in California be appealed immediately.

In the law librarians’ smackdown, all three legal research platforms gave the right answer as to the standard for appealing. However, their answers varied widely on the death knell issue and the need to file an immediate appeal — which, as Cindy Guyer, senior knowledge and research analyst at O’Melveny & Myers, the librarian who conducted the test of that question, said, is “kind of important.” 

Lexis+ AI made no mention of the death knell issue. Westlaw Precision AI did include a warning about the need for immediate appeal, but presented it in a way that was potentially confusing and might not have alerted a researcher. Only Vincent AI gave what Guyer described as a “great answer,” which included a special section that highlighted the death knell issue.

So how did OpenAI’s Deep Research do? Its full answer is reproduced below, but — spoiler alert — it picked right up on the death knell issue.

As a matter of fact, it zeroed in on this issue even before it finished its research. One of the funny things Deep Research does is offer a running commentary on its progress as it researches an issue. As you can see from the excerpt to the right, it quickly began “digging into the ‘death knell’ doctrine,” as it says.

And in the memo it produced, it gets right into the doctrine, devoting a substantial section to it right at the beginning of the memo.

Worth remembering is that Deep Research does not have access to paywalled legal research services, such as the three services in the smackdown. It conducts its research using only public-facing sources. (Ironically, perhaps, one of those sources is Casetext, the company acquired by Thomson Reuters, whose case law is still publicly accessible — for now anyway.)

One can only wonder how Deep Research would do if it could access a more robust legal research database. Would Deep Research be the death knell for commercial legal research?

Meanwhile, here is its memo, in its entirely. All of the citations were added by Deep Research.

Class certification orders in California state courts present unique challenges for appeal. Generally, California follows the “one final judgment” rule, meaning only final judgments are appealable as of right (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group). An order granting or denying class certification is interlocutory (it does not end the case), so it is not usually appealable under the final judgment rule (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group). However, California courts have developed special doctrines and procedures to allow review of class certification decisions in appropriate circumstances. This analysis outlines the California framework for appealing class certification orders, including the grounds for appeal, availability of interlocutory review, appellate courts’ standards, and the procedural steps (deadlines and filings) required to initiate an appeal.

Appealability of Class Certification Orders in California

Final Judgment Rule: Under Code of Civil Procedure § 904.1, parties generally may only appeal a final judgment or order that disposes of all causes of action (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group). A class certification order typically does not resolve the entire case; if class status is denied, the named plaintiff’s individual claims remain, and if class status is granted, the case proceeds on the merits. Thus, a class certification ruling is usually an interlocutory order not listed as directly appealable under § 904.1. California courts focus on an order’s legal effect rather than its form to determine appealability (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group). In the class context, an interlocutory order may be treated as appealable if it effectively ends the litigation for a large portion of the parties (such as absent class members), even if the named plaintiff’s claims continue (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group).

The “Death Knell” Doctrine: California’s “death knell” doctrine is the key exception that permits an immediate appeal from certain class certification orders. If a trial court denies class certification in its entirety (rejecting all class claims) and leaves only the named plaintiff’s individual claims, that order is treated as a de facto final judgment on the class issues (Litigating on the Fault Line: Class Action Law in California — Impact Fund) (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group). In this scenario, the order “effectively terminates the entire action as to the class” – in legal effect it is “tantamount to a dismissal of the action as to all members of the class other than the plaintiff” (Litigating on the Fault Line: Class Action Law in California — Impact Fund) (quoting the California Supreme Court’s description in Daar v. Yellow Cab Co.). The rationale is that without immediate review, the class claims would likely never be revived: the named plaintiff may lack a financial incentive to pursue a costly individual case to final judgment just to enable an appeal on behalf of the class (“Death Knell” Doctrine Does Not Apply When PAGA Claim Remains In Trial Court) (“Death Knell” Doctrine Does Not Apply When PAGA Claim Remains In Trial Court). Thus, as a matter of state policy, such “death knell” orders are made appealable even though they are interlocutory (Litigating on the Fault Line: Class Action Law in California — Impact Fund) (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group).

Under the death knell doctrine, an order is immediately appealable if it (1) amounts to a de facto final judgment for the absent class members, and (2) the remaining individual claims are sufficiently small or impractical that there is a risk no final judgment on those claims will ever be reached (i.e. the plaintiff might abandon the case) (Miranda v. Anderson Enterprises, Inc., 241 Cal.App.4th 196 | Casetext Search + Citator). In other words, the doctrine applies when “the persistence of viable but perhaps de minimis individual plaintiff claims creates a risk no formal final judgment will ever be entered.” (Miranda v. Anderson Enterprises, Inc., 241 Cal.App.4th 196 | Casetext Search + Citator) (quoting In re Baycol Cases I & II, 51 Cal.4th 751, 759 (2011)). California courts have emphasized that the death knell exception is limited to orders denying class certification in their entirety (Litigating on the Fault Line: Class Action Law in California — Impact Fund). Partial class certification (for example, certifying one subclass and denying another) does not trigger an immediate right to appeal because some class aspect remains alive in the case (“Death Knell” Doctrine Does Not Apply When PAGA Claim Remains In Trial Court). Likewise, if a representative claim remains that gives the plaintiff incentive to continue (such as a pending PAGA claim for civil penalties on behalf of the state), the death knell doctrine usually will not apply (“Death Knell” Doctrine Does Not Apply When PAGA Claim Remains In Trial Court). In those situations, the plaintiff can still obtain review of the class certification decision at a later final judgment, so an immediate appeal is deemed unnecessary (“Death Knell” Doctrine Does Not Apply When PAGA Claim Remains In Trial Court). By contrast, if all class and representative claims are dismissed or denied (leaving only individual issues, or sending the plaintiff to individual arbitration), then the death knell doctrine allows an immediate appeal of that order (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group) (Miranda v. Anderson Enterprises, Inc., 241 Cal.App.4th 196 | Casetext Search + Citator).

Appeal as of Right in Death Knell Cases: When the death knell doctrine applies, the class certification denial is treated as an appealable order, giving the plaintiff (or would-be class representative) a right to appeal immediately to the Court of Appeal (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group). Importantly, this appeal must be taken promptly. The appellate courts have held that if the aggrieved party does not appeal the class certification denial when it falls under the death knell doctrine, the right to appellate review is forfeited – the order becomes final and cannot be challenged later (Litigating on the Fault Line: Class Action Law in California — Impact Fund). In practice, this means a notice of appeal must be filed within the normal deadline after notice of entry of the class-certification denial (discussed below), or the opportunity for immediate review is lost. (Once a death-knell order becomes final by failure to appeal, the plaintiff generally cannot later resurrect the class claims or appeal the issue after an eventual individual judgment (Stephen v. Enterprise Rent-A-Car, 235 Cal.App.3d 806 | Casetext Search + Citator) (Stephen v. Enterprise Rent-A-Car, 235 Cal.App.3d 806 | Casetext Search + Citator).)

Orders Granting Class Certification: In contrast to denials, an order granting class certification does not qualify for the death knell exception because it does not terminate the action for anyone. Instead, it allows the case to proceed on a class basis. Such an order is considered a typical interlocutory ruling that generally must await final judgment before appellate review. Defendants (or objecting parties) do not have an automatic right to immediately appeal a class certification grant (Litigating on the Fault Line: Class Action Law in California — Impact Fund). The case will usually continue through litigation, and any challenges to the class certification (e.g. arguing the class should not have been certified) can be raised in an appeal from the final judgment. For example, if the defendant loses at trial or faces an adverse judgment in a certified class action, it can argue on appeal that the class should never have been certified, as a ground for reversing or decertifying. But there is no appeal as of right before final judgment for a certification order that keeps the lawsuit alive.

Interlocutory Review by Writ (Discretionary Review)

Although a defendant (or sometimes a plaintiff in a partial-denial scenario) cannot appeal a class certification order as of right (absent the death knell situation), interlocutory review is still possible through California’s extraordinary writ procedure. A party may file a petition for a writ of mandate (or prohibition) asking the Court of Appeal to review and overturn the trial court’s class certification ruling before the case goes to final judgment. This is an extraordinary remedy, and the appellate court has discretion on whether to grant such review – it is not guaranteed. In fact, California appellate courts exercise this discretionary review sparingly in class action matters (Litigating on the Fault Line: Class Action Law in California — Impact Fund).

A writ of mandate is essentially a request for the appellate court to intervene mid-stream on the grounds that the trial court abused its discretion or acted unlawfully in certifying or decertifying a class. Because class certification decisions are committed to the trial court’s discretion, appellate courts are hesitant to intervene absent a compelling reason. Typically, the petitioner (usually a defendant challenging a granted class certification) must demonstrate that waiting for final judgment would cause irreparable harm or undue burden, or that the class ruling presents an important legal question that merits immediate resolution. There is no formal rule (akin to Federal Rule 23(f)) in California state practice that sets specific criteria, but courts have drawn guidance from similar considerations: for example, whether the class ruling poses a “death knell” for one of the parties (e.g. exerting overwhelming pressure to settle), whether there are novel or unsettled questions of law, or clear errors that would waste resources if not corrected early (Appellate Court Provides Valuable Guidance for Interlocutory Appeals of Class Certification Orders Under Rule 23(f)) (Appellate Court Provides Valuable Guidance for Interlocutory Appeals of Class Certification Orders Under Rule 23(f)). Ultimately, the Court of Appeal has “unfettered” discretion in granting or denying a writ petition, and most petitions are summarily denied without detailed explanation (Appellate Court Provides Valuable Guidance for Interlocutory Appeals of Class Certification Orders Under Rule 23(f)) (Appellate Court Provides Valuable Guidance for Interlocutory Appeals of Class Certification Orders Under Rule 23(f)). A denial of a writ petition does not imply approval of the trial court’s ruling on the merits; it simply means the appellate court chose not to exercise immediate review. (The party can still raise the issue in a later appeal from final judgment, since a writ denial generally has no res judicata effect on the issues.)

In practice, writ relief in class certification cases is rare. California Supreme Court decisions illustrate that only exceptional cases justify mid-stream review. Sav-On Drug Stores, Inc. v. Superior Court, for example, was a case in which the defendant sought appellate review after class certification was granted; the Court of Appeal had granted a writ and reversed the class certification, but the California Supreme Court then accepted review and ultimately upheld the class certification, emphasizing the trial court’s broad discretion (Litigating on the Fault Line: Class Action Law in California — Impact Fund) (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator). This underscores that writ review will be granted only when there is a strong showing of error or an important issue – routine class certification rulings are left undisturbed until final judgment.

It is worth noting that California’s approach contrasts with federal court practice. Federal Rule of Civil Procedure 23(f) explicitly allows a party to seek permission for an interlocutory appeal of a class certification order within 14 days, and the federal appellate courts have discretion to accept or decline the appeal (Litigating on the Fault Line: Class Action Law in California — Impact Fund). California has no directly analogous rule, but the combination of the death knell doctrine (for plaintiffs facing class denial) and the writ of mandate procedure (largely used by defendants challenging class grants) serves a similar function (Litigating on the Fault Line: Class Action Law in California — Impact Fund) (Litigating on the Fault Line: Class Action Law in California — Impact Fund). The writ process is discretionary like the federal 23(f) petition, but California emphasizes that such discretionary intervention is to be granted only in exceptional circumstances (Litigating on the Fault Line: Class Action Law in California — Impact Fund).

Appellate Standards of Review for Class Certification Decisions

Whether on direct appeal (after a death-knell order or final judgment) or on a granted writ, California appellate courts apply a highly deferential standard when reviewing a class certification decision. The standard of review is abuse of discretion (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator). The trial court’s ruling on class certification will be upheld so long as it was supported by substantial evidence and founded on correct legal criteria (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator). Because trial judges are considered “ideally situated to evaluate the efficiencies and practicalities of permitting group action,” they are afforded broad discretion in deciding whether the criteria for class treatment are met (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator). An appellate court will not overturn a class certification ruling “unless (1) improper criteria were used or (2) erroneous legal assumptions were made.” (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator) In other words, a clear error of law or usage of incorrect legal standards constitutes an abuse of discretion. But if the trial court applied the proper criteria and its decision is supported by any reasonable justification, the appellate court will defer to the trial court’s judgment (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator). “Any valid pertinent reason stated will be sufficient to uphold the order.” (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator) This abuse-of-discretion review applies equally to orders granting or denying class certification. For example, a Court of Appeal reviewing a death-knell appeal of a class denial will ask if the trial court abused its discretion in finding the class criteria unsatisfied; likewise, if a defendant appeals a class certification after final judgment (or via writ), the question is whether the trial court abused its discretion in certifying the class.

It’s important to note that within this deferential framework, certain aspects can involve de novo review of legal issues. If the appeal raises a pure question of law – such as the interpretation of a statute as it affects class suitability, or whether the trial court applied an incorrect legal standard – the appellate court will review that legal issue without deference. But the ultimate decision to certify or not is reviewed for abuse of discretion, meaning factual determinations and the balancing of interests by the trial court are given great weight (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator). The California Supreme Court in Linder v. Thrifty Oil Co. and Sav-On Drug Stores reaffirmed that appellate courts should not substitute their own judgment for the trial court’s as long as the proper criteria were applied. This deference is intended to prevent “piecemeal” appeals and to recognize the trial court’s vantage point in managing class actions (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator). Consequently, when an appellate court does accept review of a class certification decision (either via death knell or writ), the hurdle to reverse the trial court’s decision is high – only a manifest abuse of discretion or legal error will justify reversal (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator).

Procedural Requirements for Appealing Class Certification Decisions

The procedure for initiating appellate review of a class certification order depends on the route of review (appeal as of right versus writ petition). In all cases, timing and proper filings are critical to invoke appellate jurisdiction. Below is an overview of the steps and deadlines:

• Notice of Appeal (Death Knell or Final Judgment): If a class certification order is immediately appealable (either under the death knell doctrine for a denial of class cert, or as part of a final judgment in the case), the party must file a timely notice of appeal in the superior court. Under California Rules of Court, Rule 8.104, a notice of appeal in a civil case generally must be filed within 60 days after the superior court clerk or a party serves the notice of entry of the judgment or appealable order, or within 180 days after entry of the order if no notice of entry was served (Rule 8.104. Time to appeal | Judicial Branch of California). This deadline is jurisdictional – an appeal filed late will be dismissed (Rule 8.104. Time to appeal | Judicial Branch of California). The notice of appeal is a simple document identifying the order or judgment being appealed (e.g. “the order denying class certification entered on [date]”). In a death knell scenario, the 60-day clock typically starts when the order denying class certification is filed and served. The appellant should be careful to specify the correct order and follow all formatting requirements of Rule 8.100 (e.g. including the names of parties, the court, etc.). Once the notice is filed, the case proceeds in the Court of Appeal on a regular briefing schedule. (The appellant must also pay the filing fee and designate the record on appeal – usually a clerk’s transcript or appendix and any reporter’s transcript of the class certification hearing, as needed to show what happened in the trial court.)
• Petition for Writ of Mandate (Interlocutory Review): To seek discretionary review of a non-appealable class certification order (for example, a defendant challenging an order granting class certification), the proper mechanism is to file a writ petition in the Court of Appeal. There is no fixed statutory deadline for a writ petition, but it must be filed within a “reasonable time” – and in practice, sooner is better. Parties often aim to file within the 60-day window analogous to a normal appeal, or even within a few weeks of the order, to strengthen the argument that prompt intervention is needed. The writ petition is a more elaborate filing than a notice of appeal: it should include a petition (often verified) explaining the case background, the relief sought, and why the trial court’s order was an abuse of discretion or legal error; a memorandum of points and authorities citing legal authority; and an appendix or exhibits containing the pertinent documents (the class certification order, the motion papers, and any relevant evidence from the record). The petition must also demonstrate why the normal appeal after final judgment would be inadequate – this is a crucial element. Typically the petitioner will argue that the class order will cause irreparable harm or unnecessary expense if not corrected immediately, or that important rights are at stake (for instance, the cost of class litigation might force a defendant to settle regardless of merits, or a plaintiff’s small claim will not proceed without class mechanism). The petition is filed directly in the Court of Appeal (with proof of service on the trial court and other parties). It is also common to simultaneously file a request for an immediate stay of trial court proceedings (such as staying notice to the class or the ongoing litigation) while the writ is under consideration. The opposing party may file a preliminary opposition in the appellate court if invited or may simply wait to see if the court requests an opposition or issues an alternative writ. If the Court of Appeal is inclined to consider the matter, it may ask for opposition (and sometimes hold oral argument) before deciding whether to grant the writ. If the writ is granted, the appellate court will issue a writ directing the trial court to vacate or modify its class certification order (or occasionally, the appellate court might simply treat the writ petition as an appeal and decide the issue on the merits). If the writ is denied (which often occurs without detailed comment), the trial court’s order stands and the case continues in the trial court; the petitioner’s only recourse at that point is to proceed to final judgment and then appeal, or to seek discretionary review in the California Supreme Court (which is rarely granted at this interim stage).
• Discretionary Review by the California Supreme Court: In exceptional instances, a party may seek review in the California Supreme Court either after the Court of Appeal’s decision on a class certification issue or directly via an original writ petition. Generally, the Supreme Court becomes involved only after the Court of Appeal has acted (for example, if the Court of Appeal published an opinion on a death knell appeal or granted a writ and decided the merits). The aggrieved party can file a petition for review to the Supreme Court within 10 days after the Court of Appeal’s decision becomes final (Rule 8.500). The Supreme Court’s review is entirely discretionary and is usually reserved for cases presenting significant legal questions or needing resolution of conflicts in the law. Historically, the California Supreme Court has taken up class certification cases to clarify standards (e.g., Linder v. Thrifty Oil Co., Sav-On Drug Stores, Brinker Restaurant Corp. v. Superior Court), but this occurs in only a small fraction of cases. For most class certification disputes, the Court of Appeal’s disposition (or lack of interlocutory review) will be the end of the road until any final judgment appeal.

In summary, appealing a class certification order in California requires careful attention to the available pathways. If the order truly sounds the “death knell” for the class, an immediate appeal as of right is available – but it must be timely pursued (Litigating on the Fault Line: Class Action Law in California — Impact Fund). Otherwise, the party must either continue litigating to final judgment and appeal then, or attempt the uphill battle of a writ petition for interlocutory relief. Throughout the process, California’s appellate courts apply a deferential standard, upholding the trial court’s decision absent a clear error or abuse of discretion (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator). This framework – grounded in case law (e.g. Daar, Richmond, Stephen, Linder, Baycol) and a few key procedural rules – balances the need to protect class litigants’ rights with the policy against piecemeal appeals. It allows truly case-ending class certification rulings to be reviewed immediately, while generally discouraging premature appeals in the many class actions that proceed toward a final judgment.

Sources:

• Code Civ. Proc. § 904.1 (appealable judgments and orders) (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group)
• Daar v. Yellow Cab Co. (1967) 67 Cal.2d 695, 699 (origin of death knell doctrine) (Stephen v. Enterprise Rent-A-Car, 235 Cal.App.3d 806 | Casetext Search + Citator)
• Richmond v. Dart Indus., Inc. (1981) 29 Cal.3d 462, 470 (class certification order appealable if it effectively dismisses class claims) (Litigating on the Fault Line: Class Action Law in California — Impact Fund)
• Stephen v. Enterprise Rent-A-Car (1991) 235 Cal.App.3d 806, 811 (appeal from class denial must be taken immediately or is waived) (Litigating on the Fault Line: Class Action Law in California — Impact Fund)
• In re Baycol Cases I & II (2011) 51 Cal.4th 751, 758-759 (California Supreme Court articulating death knell requirements: de facto final judgment for class, and remaining claims too small to ensure later review) (Miranda v. Anderson Enterprises, Inc., 241 Cal.App.4th 196 | Casetext Search + Citator)
• Munoz v. Chipotle Mexican Grill, Inc. (2015) 238 Cal.App.4th 291, 309-310 (death knell doctrine inapplicable where PAGA representative claims remained, giving plaintiff incentive to continue) (“Death Knell” Doctrine Does Not Apply When PAGA Claim Remains In Trial Court)
• Miranda v. Anderson Enterprises, Inc. (2015) 241 Cal.App.4th 196, 200 (death knell doctrine applies to dismissal of class claims; sets two-part test and notes it can apply to PAGA dismissal when individual arbitration compelled) (Dismissal of Claims for “Death Knell” Doctrine – Matern Law Group) (Miranda v. Anderson Enterprises, Inc., 241 Cal.App.4th 196 | Casetext Search + Citator)
• Sav-On Drug Stores, Inc. v. Superior Court (2004) 34 Cal.4th 319, 326, 330-332 (class certification orders reviewed for abuse of discretion; trial court’s decision will not be disturbed if it was based on proper criteria and substantial evidence) (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator) (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator)
• Linder v. Thrifty Oil Co. (2000) 23 Cal.4th 429, 435-436 (improper to deny class certification based on merits or damages considerations; reaffirming deferential review standard) (Sav-On Drug Stores, Inc. v. Superior Court, 34 Cal.4th 319 | Casetext Search + Citator).