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Stale Route-Cache Entries Survive In-Place Deploy Due To Build-Independent Cache Key In Next.Js 16.3.8

Next.js 16.3.8 introduced a regression where the route-cache key no longer depends on the build ID. In non-atomic in-place deployments that patch the .next directory without clearing .next/server/route-cache, stale cache entries reference old hashed assets, causing 404s for CSS and JS files after deployment.

highConfidence 87%Next.js Affected V16.3.8 Affected V16.4.0-Canary.60 Affected V>=16.3.8

Origin Analysis

PR #99482 changed route-cache-key.ts to generate cache keys without including a build-specific identifier. Since the route-cache directory is written at runtime and is not part of the build output, deployments that patch .next in place leave old cache files intact. The unchanged key format causes the server to continue reading stale cached responses referencing previous build assets, leading to broken pages.

1. Deploy a Next.js app with version 16.3.7; 2. Access a page that gets cached in .next/server/route-cache; 3. Upgrade to 16.3.8 without clearing route-cache; 4. Deploy new build in non-atomic mode (e.g. DeployHQ over SSH, patching only changed files); 5. Restart `next start`; 6. Request previously cached page and observe 404 for hashed CSS/JS assets.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

Reading and caching the build ID in memory works for a single build per process, but in multi-tenant or rolling update scenarios where multiple builds share a server, a process restart is required to pick up the new ID. If the code is deployed without clearing the old route-cache, the first request after upgrade will still hit the old key until the server restarts, so a restart (or automatic purge on boot) is recommended. Rollback is safe: revert the key change and manually delete .next/server/route-cache to avoid mixing old and new formats.