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nextjs - 💡(How to fix) Fix Next.js 16 increases TBT (Total Blocking Time) [1 comments, 2 participants]

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vercel/next.js#86381•Fetched 2026-04-08 02:11:19
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Code Example

This is from my local dev, although the results are seen on a live website. So Platform etc. is not relevant.

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP Tue Nov 5 00:21:55 UTC 2024
  Available memory (MB): 31662
  Available CPU cores: 32
Binaries:
  Node: 24.11.0
  npm: 11.6.1
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 16.0.3 // Latest available version is detected (16.0.3).
  eslint-config-next: N/A
  react: 19.2.0
  react-dom: 19.2.0
  typescript: 5.9.3
Next.js Config:
  output: N/A
RAW_BUFFERClick to expand / collapse

Link to the code that reproduces this issue

impossible

To Reproduce

I have a hard time saying how to reproduce this as I have a private website I cannot share, and reproducing this with a repro would be cumbersome.

I am unsure if it is related to https://github.com/vercel/next.js/issues/85470.

Current vs. Expected behavior

https://pagespeed.web.dev/ shows an increase in TBT after updating from Next.js 15 to Next.js and using cacheComponents: true where the page tested is using full static rendering during build time.

Provide environment information

This is from my local dev, although the results are seen on a live website. So Platform etc. is not relevant.

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP Tue Nov 5 00:21:55 UTC 2024
  Available memory (MB): 31662
  Available CPU cores: 32
Binaries:
  Node: 24.11.0
  npm: 11.6.1
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 16.0.3 // Latest available version is detected (16.0.3).
  eslint-config-next: N/A
  react: 19.2.0
  react-dom: 19.2.0
  typescript: 5.9.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Performance

Which stage(s) are affected? (Select all that apply)

Vercel (Deployed)

Additional context

No response

extent analysis

TL;DR

  • Investigate the impact of cacheComponents: true on Total Blocking Time (TBT) in Next.js 16.0.3.

Guidance

  • Review the discussion in https://github.com/vercel/next.js/issues/85470 to see if it relates to the TBT increase.
  • Test the performance with cacheComponents: false to isolate the effect of this setting.
  • Consider creating a minimal reproducible example to help identify the cause of the performance issue.
  • Monitor the performance metrics on the live website to see if the issue persists after making changes.

Example

  • No code snippet can be provided without more context, but testing with cacheComponents: false could be done by modifying the next.config.js file.

Notes

  • The issue may be specific to the private website's configuration or content, making it difficult to provide a general solution.
  • The relationship between cacheComponents: true and the TBT increase is not clear without further investigation.

Recommendation

  • Apply workaround: Test with cacheComponents: false to see if it improves the TBT, as this setting may be contributing to the performance issue.

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