Expanding the Core of Habeas Corpus: Diaz v. Kopp and System-Wide Conditions-of-Confinement Claims Under § 2254

1. Introduction

In Diaz v. Kopp, No. 22-1678 (2d Cir. July 30 2025), the United States Court of Appeals for the Second Circuit confronted a recurring but unsettled question: when does a state prisoner challenging conditions of confinement properly proceed by way of a habeas petition under 28 U.S.C. § 2254 rather than a civil rights action under 42 U.S.C. § 1983?

Angel Diaz, incarcerated since 1990 and suffering from hypertension and morbid obesity, alleged that during the COVID-19 pandemic the New York Department of Corrections and Community Supervision (“DOCCS”) could not constitutionally house him anywhere in its system. He therefore sought immediate release. The district court dismissed his petition as “not cognizable” in habeas, characterising it as a mis-pleaded § 1983 suit directed at prison conditions.

On appeal, a divided Second Circuit panel:

Clarified that a § 2254 petition lies at “the core of habeas” when the prisoner claims that no available facility can constitutionally confine him and release is the only remedy, even though the claim arises from conditions of confinement; but
Affirmed dismissal because Diaz failed to plead sufficient facts to make his allegations plausible.

Judge Lohier dissented, arguing the case was moot after Diaz’s transfer to another prison and the closure of the original facility. The majority opinion by Judge Calabresi thus both extends habeas doctrine and provides procedural guidance for future cases at the intersection of § 2254 and § 1983.

2. Summary of the Judgment

1. Habeas Cognisability. The court held that “at least where a petitioner alleges unconstitutional conditions that are irremediable except by release, the claim is cognizable in habeas.” A condition-of-confinement claim does not lose its habeas character merely because it references prison conditions.

2. Error Below. The district court erred in ruling, as a matter of law, that Diaz’s petition could never sound in habeas.

3. Pleading Deficiencies. Despite the legal cognisability, Diaz’s petition contained only “speculative” and “conclusory” factual allegations; he did not plausibly show that all DOCCS facilities were incapable of housing him safely. The panel therefore affirmed dismissal.

4. Mootness Rejected. The majority rejected the State’s argument that Diaz’s transfer and the closure of Sullivan Correctional Facility mooted the appeal. Because Diaz alleged system-wide incapacity, release remained a possible remedy.

5. Rule 23(a) Violation. The State transferred Diaz without first seeking leave of the Court, in tension with Fed. R. App. P. 23(a). The Court directed the clerk to substitute the warden of the new facility as respondent.

3. Analysis

3.1 Precedents Cited and Their Influence

Wilkinson v. Dotson, 544 U.S. 74 (2005) – Established that challenges to “the fact or duration of confinement” lie in habeas; others proceed under § 1983. The panel used Dotson’s “core of habeas” language as its analytical starting point.
Heck v. Humphrey, 512 U.S. 477 (1994) and Preiser v. Rodriguez, 411 U.S. 475 (1973) – Stand for habeas exclusivity when a plaintiff’s success would necessarily imply the invalidity of continued confinement. Diaz’s claim, if proven, would do exactly that.
Fielding v. LeFevre, 548 F.2d 1102 (2d Cir. 1977) – Earlier Second Circuit case holding that where unconstitutional conditions can be remedied without release, habeas is not appropriate. The majority distinguished Fielding because Diaz alleged no remedial conditions exist anywhere.
Out-of-Circuit COVID decisions: Hope v. Warden (3d Cir. 2020); Wilson v. Williams (6th Cir. 2020); Pinson v. Carvajal (9th Cir. 2023). The panel aligned itself with circuits that allow habeas for claims that “no set of conditions would be constitutionally sufficient.”
Longway v. Jefferson Cnty., 24 F.3d 397 (2d Cir. 1994) and McCray v. Lee, 963 F.3d 110 (2d Cir. 2020) – Address mootness upon transfer; the majority distinguished them by interpreting Diaz’s allegations as system-wide, not facility-specific.

3.2 The Court’s Legal Reasoning

Liberal Construction of Pro Se Pleadings. Because Diaz filed pro se, the panel read his petition “to raise the strongest argument it suggests.” This flexible reading allowed the court to treat vague references to “DOCCS facilities” as an assertion that no state facility could protect him.
Defining the “Core” of Habeas. The majority articulated a two-part test for when a conditions claim falls in habeas: (i) the claim alleges a constitutional violation in custody itself (Eighth Amendment), and (ii) release is required, not merely preferable. The court emphasised that § 2254’s statutory text is broad (“in custody in violation of the Constitution”), unlike § 2255’s narrower wording.
Interaction with § 1983. The decision rejects a categorical rule that all conditions claims are § 1983 actions, yet also rejects the petitioner’s argument that any request for release must be habeas. Instead, courts must examine whether alternative injunctive relief could suffice. If transfer, segregation, vaccination, or other measures could cure the violation, § 1983 is the correct vehicle; otherwise, habeas is.
Rule 12-Style Screening. Though cognisable, the petition failed on the pleadings. The Rules Governing § 2254 Cases (Rules 2 & 4) require facts that “state a claim to relief that is plausible on its face.” Diaz’s “fundamental nature” allegations lacked facility-wide data, infection statistics, or proof that vaccination and mitigation were impossible.
Mootness & Rule 23(a). The majority viewed the State’s unauthorised transfer as procedurally improper but not jurisdiction-defeating. Because relief—release—remained possible, the court retained Article III jurisdiction. Judge Lohier’s dissent found the opposite, concluding that Diaz’s counsel narrowed the claim to Sullivan-specific conditions, rendering the appeal moot.

3.3 Potential Impact of the Decision

Broader Access to Habeas for Conditions Cases. Prisoners alleging systemic, irremediable Eighth Amendment violations may now frame claims as § 2254 petitions in the Second Circuit. This could increase habeas filings, especially in health crises or where prison infrastructure is uniformly deficient.
Strategic Pleading Considerations. Counsel must evaluate whether to allege that no alternative set of conditions exists. Doing so opens habeas but also imposes stricter pleading burdens and potential AEDPA constraints.
PLRA Work-Around Debate. The Prison Litigation Reform Act (PLRA) does not apply to habeas proceedings. States may argue, as New York did, that allowing conditions claims through habeas circumvents PLRA’s exhaustion and remedial limits. The panel dismissed that concern, citing the PLRA’s express habeas carve-out (§ 3626(g)). Future litigation may test where the line truly lies.
Transfer Protocol Enforcement. The emphatic reference to Rule 23(a) signals that appellate courts will scrutinise state transfers of habeas petitioners. Failing to seek leave may result in respondent substitution and, implicitly, disapproval.
Split Within the Circuit. Judge Lohier’s dissent underscores an unresolved tension: whether a counseled narrowing of claims on appeal can moot a case. District courts may confront similar debates about the binding nature of pro se pleadings versus superseding counseled arguments.

4. Complex Concepts Simplified

Habeas Corpus (28 U.S.C. § 2254). A legal mechanism allowing state prisoners to ask a federal court to order their release when they are “in custody in violation of the Constitution or laws or treaties of the United States.” Think of it as a special kind of lawsuit directly attacking the prisoner’s confinement itself.
42 U.S.C. § 1983. A general civil rights statute permitting suits against state officials for constitutional violations. Unlike habeas, it usually seeks damages or injunctive relief other than release.
“Core of Habeas.” Supreme Court shorthand for claims that challenge the fact or duration of custody so that success would necessitate release or a shorter sentence.
Prison Litigation Reform Act (PLRA). Federal law (18 U.S.C. § 3626) that limits court remedies—and imposes exhaustion and filing fees—when prisoners sue about prison conditions. It does not apply to habeas corpus petitions.
Mootness. A case becomes moot when the court can no longer provide meaningful relief. Federal courts may not issue advisory opinions on moot claims.
Fed. R. App. P. 23(a). Requires that a prisoner “not be transferred” during a pending habeas appeal without first seeking the appellate court’s permission, ensuring the court’s jurisdiction and ability to grant effective relief.

5. Conclusion

Diaz v. Kopp is most significant for its doctrinal clarification: a prisoner may press a system-wide, irremediable conditions-of-confinement claim through § 2254 when release is the only remedy that would cure the constitutional violation. The decision:

Rejects the categorical view that conditions claims always belong under § 1983;
Confirms that the remedy sought is not solely dispositive—courts must ask whether any constitutional conditions are feasible;
Highlights procedural safeguards for pro se litigants and underscores liberal construction principles;
Warns states to comply with Rule 23(a) when transferring habeas petitioners; and
Leaves open factual hurdles: petitioners must plausibly allege systemic incapacity, not speculation.

Going forward, litigators should treat Diaz as a roadmap: if they can credibly claim that no alternative conditions exist, habeas is available—yet success will hinge on robust factual development. For courts, the opinion balances doctrinal clarity with practical caution, affirming dismissal where pleadings are thin while expressly welcoming stronger cases that meet the newly articulated standard.