Add allotment carryover behavior note to Product Allotments page

[goldstarrr]

What does this PR do?

Adds a note to the "Allotments by parent products" section of the
Product Allotments
page documenting an upcoming change to how allotments are calculated.

Beginning August 2026, for products whose usage is cumulative over the month
(for example, Ingested Spans and Indexed Spans), allotments will apply across
the whole billing period instead of hour by hour, so unused allotment can carry
over to other hours within the same billing period. The note also clarifies:

• Products measured on a concurrent count, peak, or average (hosts, containers,
  custom metrics) are unchanged.
• Usage billed through an external marketplace (AWS, Azure, GCP) is unchanged.
• Allotments still do not carry over between billing periods.
• Accounts transition on a rolling basis, indicated by a banner in Plan & Usage.

Also softens the existing "allotments are not carried over to subsequent hours"
sentence to "generally not carried over" so it no longer conflicts with the new note.

Motivation

Documents the upcoming allotment calculation change ahead of the rolling rollout
so customers and support have an accurate reference.

Additional Notes

• Single file changed: content/en/account_management/billing/product_allotments.md
• Content reviewed internally by product before submission.
• Target publish: 2026-08-03

[maxvp]

/review

[github-actions]

🤖 Automated review by Claude. AI-generated; verify before acting.

A few style-guide nits: temporal phrasing (will, in the future) and the **Note**: callout format. Content itself reads clearly and the table example is a helpful addition.

_{Reviewed 102cb111f4aad23d917139e9b74c1c03e55dc9f7 — workflow run}

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/sgoldman/allotment-carryover-note/account_management/billing/product_allotments

[maxvp]

Hi @goldstarrr, apologies as I accidentally merged this prior to the Aug 3 target date. I submitted #38536 to revert the change. Once the date comes, we can un-revert it to publish the content from this PR.

[goldstarrr]

Hi @goldstarrr, apologies as I accidentally merged this prior to the Aug 3 target date. I submitted #38536 to revert the change. Once the date comes, we can un-revert it to publish the content from this PR.

No problem, if possible can we merge friday? I will be out of office but if someone on the docs team could merge it then that would be awesome.