{"rewrite":{"id":"r_6e02e28e4ba9391ac083f23d","clusterId":"c_c5737d51ddeb9039c2de661f","slug":"amd-details-instinct-mi400-architecture-and-helios-rack-at-hot-chips-2026","model":"deepseek-v4-1-flash","headline":"AMD Details Instinct MI400 Architecture and Helios Rack at Hot Chips 2026","summary":"At Hot Chips 2026, AMD gave two talks on the Instinct MI400, covering the GPU's internal structure and the system architecture for the Helios rack. The MI400 moves the XCDs to TSMC N2 and the IODs to N3P, splits the Infinity Cache into a separate FCD, carries 12 HBM4 stacks, and adds 72 lanes of UALoE alongside PCIe, with PCIe, UALink and UALoE switched at the protocol level.","whyItMatters":"AMD's split-chip MI400 layout, a larger HBM4 load and Ethernet-carried UALoE point to rack-scale link design as the contested ground in the next accelerator generation, rather than the single die.","webCardHtml":"\u003cp\u003eThe Instinct MI400 totals 12 chiplets. Eight XCDs sit on top of the FCD, and the separate IOD connects alongside them.\u003c/p\u003e\u003cp\u003eThe Infinity Cache drops from 256MB across the MI350 series to 192MB, split into 96 1MB blocks per FCD, with HBM4 capacity and bandwidth rising to compensate. Each XCD carries 34 WGPs with 32 enabled, giving 256 WGPs across the package, which AMD counts as the equivalent of 512 CUs. The LDS grows from 160KB to 384KB.\u003c/p\u003e","blueskyPost":"AMD's MI400 puts 72 UALoE lanes next to PCIe and switches PCIe, UALink and UALoE at the protocol level. That is a bet the rack fabric, not the GPU die, decides who scales.","twitterPost":"AMD's MI400 adds 72 UALoE lanes alongside PCIe. The rack fabric, not the GPU die, is where scale gets decided.","threadsPost":"AMD's MI400 carries 12 HBM4 stacks and moves its compute dies to TSMC N2, but the part that shapes deployments is 72 lanes of UALoE switched at the protocol level with PCIe and UALink. Rack interconnect is where scaling gets decided now.","newsletterBlurb":"AMD used Hot Chips 2026 to walk through the Instinct MI400's chiplet layout and the Helios rack system around it. The XCDs move to TSMC N2, the IODs to N3P, and the Infinity Cache is split onto a separate FCD at 192MB total. The I/O side carries 72 lanes of UALoE, with PCIe, UALink and UALoE switched at the protocol level.","attributionJson":"[{\"source\":\"ASCII.jp\",\"url\":\"https://ascii.jp/elem/000/004/445/4445476/?rss\",\"title\":\"The Practical Answer to NVLink Pursuit: \\\"UALoE\\\" - AMD Instinct MI400 Takes On Next-Generation Rack Implementation and Rivals Blackwell\"}]","lintFlagsJson":null,"lintHits":0,"costUsd":0,"inputTokens":4822,"outputTokens":683,"status":"published","repairAttempts":0,"nextRepairAt":null,"factsAttemptedAt":1792986579,"createdAt":"2026-10-26T03:44:12.000Z","publishedAt":"2026-10-26T03:48:35.000Z","updatedAt":"2026-10-26T03:48:35.000Z"},"cluster":{"id":"c_c5737d51ddeb9039c2de661f","canonicalTitle":"NVLink追撃の現実解「UALoE」　AMD Instinct MI400が挑む次世代ラック実装とBlackwell対抗","representativeArticleId":"a_2ee78422acb733a40b52096d","sourceCount":1,"writtenSourceCount":1,"writeAttempts":0,"isSolo":true,"entitiesJson":"{\"anime_titles\":[],\"manga_titles\":[],\"work_titles\":[\"AMD Instinct MI400\"],\"studios\":[\"AMD\"],\"people\":[],\"type\":\"news\",\"domain\":\"other\",\"is_roundup\":false}","contentType":"news","status":"published","firstSeenAt":"2026-10-26T03:00:00.000Z","lastSeenAt":"2026-10-26T03:00:00.000Z","updatedAt":"2026-10-26T03:48:34.000Z"},"attribution":[{"source":"ASCII.jp","url":"https://ascii.jp/elem/000/004/445/4445476/?rss","title":"NVLink追撃の現実解「UALoE」　AMD Instinct MI400が挑む次世代ラック実装とBlackwell対抗"}],"entities":{"anime_titles":[],"manga_titles":[],"work_titles":["AMD Instinct MI400"],"studios":["AMD"],"people":[],"type":"news","domain":"other","is_roundup":false},"keyFacts":null,"pageLinks":{"healthSlugs":["amd-instinct-mi400","amd"],"storySlugs":[],"entities":[{"slug":"amd-instinct-mi400","supported":1,"disputed":0,"contradicted":0,"unverified":5,"overall":"green","story_count":1,"has_dossier":false},{"slug":"amd","supported":1,"disputed":0,"contradicted":0,"unverified":4,"overall":"green","story_count":6,"has_dossier":true}],"stories":[],"entitiesOk":true,"storiesOk":true}}