✨ feat: enable LCP subparts collection by default

[HugoGarrido]

Motivation

This PR enables by default LCP subparts collection without the need for any feature flag
The code has been introduced in this PR
And the change is available behind a flag since v6.27.0 (release notes)

How to query in RUM

# Load Time
@view.performance.lcp.sub_parts.load_time:*

# Load Delay
@view.performance.lcp.sub_parts.load_delay:*

# Render Delay
@view.performance.lcp.sub_parts.render_delay:*

# TTFB (pre-existing)
@view.first_byte:*

Changes

• Remove code gated behind ExperimentalFeature.LCP_SUBPARTS
• LCP subparts are now collected by default

Test instructions

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[datadog-prod-us1-4]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 77.32% (-0.01%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: f9fa062 | Docs | Datadog PR Page | Was this helpful? React with 👍/👎 or give us feedback!}

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	176.56 KiB	176.49 KiB	-65 B	-0.04%	✅
Rum Profiler	6.16 KiB	6.16 KiB	0 B	0.00%	✅
Rum Recorder	27.46 KiB	27.46 KiB	0 B	0.00%	✅
Logs	56.88 KiB	56.85 KiB	-30 B	-0.05%	✅
Rum Slim	132.19 KiB	132.13 KiB	-57 B	-0.04%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Pending...

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	27.95 KiB	26.67 KiB	-1.27 KiB
RUM - add action	92.80 KiB	51.03 KiB	-41.76 KiB
RUM - add timing	26.14 KiB	26.72 KiB	+588 B
RUM - add error	101.44 KiB	55.53 KiB	-45.91 KiB
RUM - start/stop session replay recording	25.82 KiB	26.76 KiB	+961 B
RUM - start view	470.17 KiB	466.17 KiB	-4.01 KiB
Logs - log message	44.16 KiB	44.82 KiB	+676 B

🔗 RealWorld

[HugoGarrido]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

browser-sdk/packages/core/src/tools/experimentalFeatures.ts

Line 16 in f9fa062

export enum ExperimentalFeature {

Preserve removed experimental enum member

Removing ExperimentalFeature.LCP_SUBPARTS from the exported ExperimentalFeature enum introduces a source-compatible break for TypeScript consumers of @datadog/browser-core that still reference ExperimentalFeature.LCP_SUBPARTS in their configs/tests; after upgrading, their builds will fail even though the runtime behavior is now default-on. Keeping the enum member as a deprecated no-op alias avoids this upgrade break while still enabling subparts by default.

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[BenoitZugmeyer]

Could you adjust the PR title? 💥 is reserved for breaking changes, ✨ is for features.

[HugoGarrido]

Could you adjust the PR title? 💥 is reserved for breaking changes, ✨ is for features.

Done! I was not sure since I'm removing a value from an enum if it was considered a breaking change or not

[HugoGarrido]

/merge

[gh-worker-devflow-routing-ef8351]

View all feedbacks in Devflow UI.

2026-03-25 09:33:17 UTC ℹ️ Start processing command /merge

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2026-03-25 09:33:21 UTC ℹ️ MergeQueue: pull request added to the queue

The expected merge time in main is approximately 1h (p90).

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2026-03-25 10:09:22 UTC ℹ️ MergeQueue: This merge request was merged