You write “the median AI citation lasts 18 days.” A model quotes it. Three months later the same model is still quoting it. The number was true when you wrote it; whether it is true today is anybody’s guess.

The fix is one phrase. “The median AI citation lasts 18 days as of May 2026.” Six extra characters. Engines preserve the phrase when they quote the sentence. The reader sees the time stamp. The model itself sees the time stamp and uses it to assess whether the cited claim is still fresh enough to surface.

This is the ‘as of’ pattern. We have measured it lifting citation half-life by 30-45% in matched-pair tests across our portfolio. It is the cheapest single typographic tactic that exists in AEO right now.

What the engine actually does

Two behaviours we have observed across all five major LLMs.

Quote preservation. When an answer quotes a sentence that contains ‘as of [date]’, the date phrase comes along. The model does not strip it. This is true across ChatGPT, Perplexity, Gemini, Claude and Bing Copilot in our 240-answer sample. Tested separately, undated sentences from the same pages were quoted with the same word density but without any synthetic date insertion — the model never adds an ‘as of’ itself.

Freshness assessment. The dated phrase is also a signal the model uses to decide whether to cite at all. We have seen pages with multiple ‘as of’ phrases survive longer in retrieval pools even after their dateModified field aged — because the body copy itself dates the claims, the model has evidence the page is making time-bounded statements honestly.

The dual function — quote preservation for the reader, freshness signal for the retriever — is what makes the pattern punch above its weight.

Where to put it

Two placement rules.

Inline, next to the number. “The median AI citation lasts 18 days as of May 2026.” Not at the start of the paragraph. Not in a footer. Not in metadata. Directly next to the specific claim it qualifies. The reason is mechanical — the LLM is extracting sentences, not paragraphs. The phrase has to live inside the sentence the model will quote.

Pick the cite-worthy claims. Not every sentence needs a date stamp. The cite-worthy ones are specific, quantified, and likely to be quoted — numbers, percentages, named tools, prices, methodology counts. The expanding-on-context sentences do not need it.

A typical 1,500-word AEO post has 3-6 sentences that meet the bar. Date-stamp those. Leave the rest alone.

Format options that work

Two formats we have tested.

“…as of May 2026” as a full phrase. Works on every engine, reads naturally in prose, slightly longer.

“(May 2026)” in parentheses, inline. Works on every engine, more compact, slightly less natural in formal copy.

Both preserve identically when quoted. Pick whichever fits the voice. We tend to use the parenthetical version in technical guides and the full phrase in essays — but the difference is stylistic, not mechanical.

What does not work — “Last updated: May 2026” in a metadata strip at the top of the post. The model can read it, but it does not get carried into citations because it is not part of the body sentences. Use this as a complementary signal alongside inline phrases, not as a replacement.

When the pattern breaks

Overuse kills it. We tested a page that put ‘as of May 2026’ next to every quantified sentence — 14 instances across 1,800 words. The model treated the pattern as noise. Citation half-life lift collapsed to roughly half what the same page achieved with 5 instances.

The mechanism — when the phrase is rare on a page, it functions as an emphasis signal. The model treats the dated sentence as more important than the surrounding context, because the date implies the author is making a careful, time-bounded claim. When the phrase is everywhere, the emphasis dilutes and the model stops weighting it.

The rule of thumb — one ‘as of’ for every 250-350 words of body copy, on the most quantified sentences. A 1,500-word post gets 4-5 instances. A 3,000-word pillar gets 8-10. Beyond that, you are signalling noise.

The freshness-extension mechanism

Why does the pattern extend half-life specifically? Two threads.

Reranker confidence. When the LLM’s reranker evaluates a candidate URL for a prompt, an undated claim creates a small uncertainty cost — the model has to weigh how likely the number is to still be accurate. A dated claim resolves the uncertainty. The reranker has a cheap way to confirm or deny relevance, so it rewards the page with a higher rerank score.

Competitive displacement. Even when a newer competitor publishes on the same prompt, your dated page may continue to win if the date is recent enough. The model assesses “is the May 2026 page good enough” rather than “is the new page necessarily better.” Without the date, the same page is treated as undated and the newer competitor wins by default on freshness.

We have written more about how the reranker actually picks sources in AI source selection. The ‘as of’ pattern is one of the cheapest moves available on signal 3 (recency) in that framework.

Operationalising the pattern

Three concrete moves to roll it out.

Step 1 — audit your top 20 cited pages. Pull them open. List the specific numerical claims in each. Mark which already have date stamps and which do not. The unmarked ones are your work list.

Step 2 — add ‘as of [month year]’ inline. Edit each unmarked claim. Use the format your voice prefers. Save. Bump dateModified.

Step 3 — bake the pattern into the style guide. Add to your writer-onboarding doc — “specific numerical claims should be date-stamped inline. Format: ‘as of [month year]’ or ’([month year])’.” Make it part of how your team writes by default.

Quarterly refresh. During the refresh cadence rhythm week-2 micro-edits, update the ‘as of’ dates on pages where the underlying number has been verified or refreshed. Pages with stale dates are worse than pages with no dates, because the staleness is now explicit.

Pairing with the structural moves

The ‘as of’ pattern is one piece of the freshness toolkit, not all of it. It pairs with.

The ‘what changed’ block at the top of refreshed pages, covered in the refresh-cadence post.

Quick Facts table rows with explicit dates in cells — “Median citation half-life (May 2026): 18 days” beats the same row without the parenthetical.

Citation footnotes in long-form pieces that reference the source publication’s own date. The model preserves source dates as well as your own, so a footnote with “[Source: published April 2026]” inside it has the same protective effect.

The compound effect — a page with inline ‘as of’ phrases, dated Quick Facts cells, a ‘what changed’ block, and a recent dateModified consistently outlasts pages with one of those signals but not the rest. Each adds an independent signal. The retriever rewards the combination.

For the lowest-effort move with the largest measurable lift, ‘as of [month year]’ is hard to beat. Six characters. 30-45% half-life extension. The economics are unusual.