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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Intl.DateTimeFormat('de-CH', {year, month}) outputs different separators between Node 24.13.0 and 24.13.1","articleBody":"### Version\n\n24.13.1\n\n### Platform\n\n```text\nDarwin N22134 25.3.0 Darwin Kernel Version 25.3.0: Wed Jan 28 20:48:41 PST 2026; root:xnu-12377.81.4~5/RELEASE_ARM64_T6041 arm64\n```\n\n### Subsystem\n\n_No response_\n\n### What steps will reproduce the bug?\n\nIntl.DateTimeFormat produces inconsistent formatting for partial date options (year + month) between Node 24.13.0 and 24.13.1.\n\t•\tNode 24.13.0 outputs '12.2021' (dot separator) as expected for de-CH.\n\t•\tNode 24.13.1 outputs '12/2021' (slash separator) for the same code.\n\t•\tAdding day: '2-digit' produces consistent '07.12.2021' in both versions.\n\nThis behavior change breaks SSR/client hydration in frameworks like Next.js when formatting dates for de-CH locale.\n\nReproduction:\n\n```js\n// Test partial month/year formatting\nconsole.log(\n  new Intl.DateTimeFormat('de-CH', { year: 'numeric', month: '2-digit' }).format(new Date(\"2021-12-07\"))\n);\n\n// Test full date formatting\nconsole.log(\n  new Intl.DateTimeFormat('de-CH', { year: 'numeric', month: '2-digit', day: '2-digit' }).format(new Date(\"2021-12-07\"))\n);\n```\n\n### How often does it reproduce? Is there a required condition?\n\nAlways\n\n### What is the expected behavior? Why is that the expected behavior?\n\nBoth Node versions should produce '12.2021' for { year, month } in de-CH locale.\nSeparator should follow locale conventions consistently, even for partial formats.\n\n### What do you see instead?\n\nNode 24.13.1 outputs '12/2021'\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/talamcol","@type":"Person","name":"talamcol"},"datePublished":"2026-02-17T08:54:10.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/61861/node/issues/61861"}