Joao Carlos de Novaes v Caixa Economica Federal
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João Carlos de Novaes and others v. Caixa Econômica Federal is a Brazilian appeal concerning monetary correction and interest in judgment enforcement. Its AI-related issue arose from hidden instructions in an appellate filing. On October 20, 2026, the First Panel of the Superior Court of Justice (STJ) unanimously denied the internal appeal and imposed a personal fine totaling R$20,000 on counsel for conduct against the dignity of justice. The hidden content did not affect the appeal’s outcome.[2] [3] [4]
Underlying dispute and procedural history
The appellants challenged the use of the Federal Justice calculations manual after the disappearance of the BTN monetary index, and the application of Selic interest in calculating the judgment debt. The Federal Regional Court of the Third Region had upheld the judicial accounting. The STJ rapporteur’s vote rejected the internal appeal on ordinary procedural grounds, including the bar on reexamining facts and evidence and the failure to preserve specified federal-law questions for review. These grounds are distinct from the filing-conduct sanction.[2]
The STJ docket records electronic receipt from the lower court on October 28, 2025 and registration on November 4, 2025. It records the STJ president’s January 15, 2026 decision not to entertain the special appeal, an internal appeal filed February 12, and the First Panel’s unanimous October 20 disposition. As reviewed October 21, the latest entry sends the panel judgment for publication expected October 23; it does not establish finality or the outcome of any later challenge.[4]
October 20, 2026 hidden-prompt sanction
The vote describes a September 25 technical certification identifying two copies of concealed text in the special-appeal petition. Both used 0.8-point lettering; one was white on white, and the other matched a decorative footer. The instructions sought favorable treatment of admissibility and the appeal’s outcome. The vote treats this as an attempt to influence automated preparatory analysis, rather than ordinary visible legal argument.[2]
The signing lawyer said he coordinated, signed and filed the petition, while the other counsel did not participate in its preparation. He denied any intent to manipulate court AI, suggested residual AI drafting text, and relied on tests in which STJ Logos treated the commands as petition text without influencing its analysis. The vote rejected that explanation as insufficient to account for the two separate concealment methods. It distinguished permissible AI assistance in drafting from concealed instructions aimed at the court’s tools; successful manipulation was not required for the sanction.[2]
The vote relies on procedural good faith and duties of candor and cooperation, including Civil Procedure Code article 77, IV and VI. It places responsibility for the integrity of an electronically signed filing on counsel. The R$20,000 amount is the total personal fine imposed on the lawyers constituted in the case, rather than R$20,000 per lawyer or a fine on the represented parties. Individual responsibility for disciplinary or criminal purposes was left for the appropriate authorities.[2]
The disposition also calls for preservation of the native file, its hash and extracted text, and a technical report documenting the hidden material, location, typography, file provenance and integrity. It directs copies to the Paraná section of the Brazilian Bar Association (OAB) and the Federal Prosecution Service (MPF) for assessment within their respective powers. Those referrals are not findings that disciplinary or criminal liability has been established.[2][3]
Related articles and coverage
References
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 STJ, Paulo Sérgio Domingues, rapporteur’s vote in AgInt no AREsp 3.095.458/SP, pp. 1–21, linked from the court’s October 20, 2026 report.
- ↑ 3.0 3.1 STJ, “Novo caso de prompt injection: STJ multa advogados em R$ 20 mil por ato contra a dignidade da Justiça,” October 20, 2026.
- ↑ 4.0 4.1 STJ public docket, AREsp 3095458/SP (2025/0422819-8), Details and Phases, reviewed October 21, 2026.