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partial fallbacks: gate behind experimental flag#91123

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ztanner merged 1 commit intocanaryfrom
03-09-partial_fallbacks_gate_behind_experimental_flag
Mar 9, 2026
Merged

partial fallbacks: gate behind experimental flag#91123
ztanner merged 1 commit intocanaryfrom
03-09-partial_fallbacks_gate_behind_experimental_flag

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@ztanner ztanner commented Mar 9, 2026 •
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This puts the partial fallback upgrading feature introduced in #89063 behind a flag to make it easier to test the rollout/eventual stabilization in isolation.

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ztanner commented Mar 9, 2026

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@ztanner ztanner marked this pull request as ready for review March 9, 2026 22:17
@ztanner ztanner requested a review from ijjk March 9, 2026 22:17
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ijjk reviewed Mar 9, 2026
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@ztanner ztanner force-pushed the 03-09-partial_fallbacks_gate_behind_experimental_flag branch from 5f99cd3 to 16d9a77 Compare March 9, 2026 22:35
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Stats from current PR

✅ No significant changes detected

📊 All Metrics
📖 Metrics Glossary

Dev Server Metrics:

  • Listen = TCP port starts accepting connections
  • First Request = HTTP server returns successful response
  • Cold = Fresh build (no cache)
  • Warm = With cached build artifacts

Build Metrics:

  • Fresh = Clean build (no .next directory)
  • Cached = With existing .next directory

Change Thresholds:

  • Time: Changes < 50ms AND < 10%, OR < 2% are insignificant
  • Size: Changes < 1KB AND < 1% are insignificant
  • All other changes are flagged to catch regressions

⚡ Dev Server

Metric Canary PR Change Trend
Cold (Listen) 914ms 913ms ✓ ▁▆▁▁▁
Cold (Ready in log) 900ms 898ms ✓ ▁▄▁▁▁
Cold (First Request) 1.660s 1.656s ✓ ▂▄▂▂▂
Warm (Listen) 912ms 914ms ✓ ▁▅▁▁▁
Warm (Ready in log) 899ms 902ms ✓ ▁▄▁▁▁
Warm (First Request) 713ms 719ms ✓ ▁▃▁▁▁
📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric Canary PR Change Trend
Cold (Listen) 455ms 455ms ✓ ▁▁█▁▁
Cold (Ready in log) 433ms 434ms ✓ ▄▄█▂▄
Cold (First Request) 1.835s 1.848s ✓ ▂▂█▂▂
Warm (Listen) 457ms 456ms ✓ ▁▁█▁▁
Warm (Ready in log) 434ms 434ms ✓ ▃▃█▂▄
Warm (First Request) 1.842s 1.846s ✓ ▂▂█▂▂

⚡ Production Builds

Metric Canary PR Change Trend
Fresh Build 6.419s 6.260s ✓ ▁▄▁▁▁
Cached Build 6.218s 6.079s ✓ ▁▄▁▁▁
📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric Canary PR Change Trend
Fresh Build 13.873s 13.867s ✓ ▁▁█▂▁
Cached Build 14.092s 14.048s ✓ ▁▁█▂▁
node_modules Size 477 MB 477 MB ✓ █████
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Bundle Sizes

⚡ Turbopack

Client

Main Bundles: **402 kB** → **402 kB** ✅ -11 B

80 files with content-based hashes (individual files not comparable between builds)

Server

Middleware
Canary PR Change
middleware-b..fest.js gzip 764 B 766 B ✓
Total 764 B 766 B ⚠️ +2 B
Build Details
Build Manifests
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Canary PR Change
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Canary PR Change
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Canary PR Change
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Server

Edge SSR
Canary PR Change
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Canary PR Change
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Canary PR Change
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Canary PR Change
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🔄 Shared (bundler-independent)

Runtimes
Canary PR Change
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📝 Changed Files (1 file)

Files with changes:

  • server.runtime.prod.js
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📎 Tarball URL 
https://vercel-packages.vercel.app/next/commits/16d9a77858b444e351b902c6f7342bb7460f179c/next

@ztanner ztanner merged commit c0bf4b6 into canary Mar 9, 2026
159 checks passed
@ztanner ztanner deleted the 03-09-partial_fallbacks_gate_behind_experimental_flag branch March 9, 2026 22:58
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