The modern equivalent of "what does Google rank first" is "what does ChatGPT cite first." The question has an answer, and the answer is neither open, neutral, nor stable.

For a generation, Google PageRank was the most consequential algorithm in information distribution. It decided which pages surfaced first, and in doing so decided which institutions, brands, and individuals were visible. Every communications strategy, every SEO budget, every earned-media placement, every Wikipedia entry was built around a single foundational question: what does PageRank reward?

That question is now a legacy question. Its successor is more consequential, more measurable, and far less well understood: what do ChatGPT, Claude, Gemini, Perplexity, and Google AI Overviews actually cite when they assemble an answer? Between August 2024 and April 2026, six of the largest citation-tracking studies ever conducted produced overlapping datasets covering more than 680 million individual citations. Everything-PR Research has synthesized that data into the first consolidated ranking of the fifty sources that compose the modern AI answer.

The findings contradict most prevailing assumptions about AI behavior. Platforms do not treat the open web as a level playing field. They concentrate citation share in a remarkably small set of domains. They privilege user-generated community content over most institutional journalism. They treat a single encyclopedia as near-foundational training material. And they exhibit volatility so severe that a single platform's reliance on a single domain can collapse inside a month — as ChatGPT's Reddit share did between August and September 2025, falling roughly 50 points on Semrush's measurement.

For communicators, publishers, educators, institutions, and brand owners, this is the working map of the new discovery terrain. The organizations that understand it will compound visibility over the next 24 months. The organizations that do not will discover, too late, that they have been running campaigns against a set of rules whose mechanics were already documented.

Methodology

This index synthesizes verified citation data from six of the largest published studies of generative AI citation behavior conducted between August 2024 and April 2026, covering more than 680 million individual citations across the five dominant AI answer engines.

Source studies and scope

• Profound's longitudinal citation study (August 2024 – October 2025), covering 680 million+ citations across ChatGPT, Google AI Overviews, and Perplexity, with updates through Reddit's own Q2 2025 shareholder disclosure.
• Semrush analyses of 150,000 citations (June 2025) and 230,000 prompts over 13 weeks (August – November 2025), documenting citation volatility after the September 2025 Google num=100 parameter change.
• Ahrefs Brand Radar analysis of the 100 most-cited domains in ChatGPT (September 2025), broken out by US and global coverage.
• Search Engine Land consolidated cross-platform analysis (October 2025), covering Reddit, YouTube, LinkedIn, Wikipedia, and Forbes as the leading multi-platform citation sources.
• Muck Rack's journalism citation study (July 2025), analyzing more than one million citations to measure how often AI platforms rely on journalistic content and which publishers are cited most.
• Visual Capitalist's synthesis of LLM citations across more than 150,000 queries (August 2025), documenting aggregate ranked frequency data.

Everything-PR Research consolidated these studies into a cross-referenced citation-share signal — defined as the average rank position of each domain across the source studies, weighted by each study's citation volume — and constructed a ranked index of the 50 domains that collectively define the modern AI answer. We grouped the index into six functional categories — Community & Conversation, Encyclopedic & Reference, Professional & Identity, Video & Audio, Editorial & News, and Commerce & Review — to reflect the distinct strategic approaches each category requires. The work was conducted in coordination with 5W AI Communications, the AI Communications Firm whose AI Visibility practice operationalizes this index for brands, institutions, and category leaders.

Four structural findings that will shape AI visibility strategy through 2027.

What communications, PR, and institutional leaders should do with this map.

1. Audit presence across the top fifteen sources before the long tail. An organization without verified presence across Reddit, Wikipedia, YouTube, LinkedIn, Forbes, Reuters, and four to five category-specific domains is invisible to 68% of the AI citation pipeline.
2. Build Wikipedia as infrastructure, and resource it accordingly. ChatGPT cites Wikipedia at 26–48% of its top-10 share.
3. Treat Reddit as a strategic channel, not a tactical one. Reddit is the single most-cited domain across AI platforms. See the 50 subreddits AI engines cite most.
4. Map journalism targets to platform-specific citation patterns. ChatGPT favors Forbes, Business Insider, Reuters. Perplexity favors NIH, Microsoft, Britannica. Claude favors NYT, Atlantic, New Yorker, Economist.
5. Treat LinkedIn as a citation channel, not a social-media channel. LinkedIn is a top-five multi-platform citation source.
6. YouTube is the only serious video-citation asset. Any video-content strategy that does not prioritize YouTube is not a serious AI visibility strategy.
7. Plan for volatility, not stability. Diversification across the top fifteen sources is no longer optional; it is risk management.

Operating Model and Engine Guides

The Index maps where engines pull from. The operating model for earning a place in those sources is the GEO Operating Stack. Engine-by-engine playbooks:

• How to Rank on ChatGPT · ChatGPT Citation Source Index 2026
• How to Rank on Claude · Claude Citation Source Index 2026
• How to Rank on Gemini · Gemini Citation Source Index 2026
• How to Rank on Perplexity · Perplexity Citation Source Index 2026
• How to Rank on Google AI Overviews and AI Mode · Google AI Overviews Citation Source Index 2026

Practitioner companion: How PR Teams Use Claude — the working guide for communications professionals using Claude inside daily workflows: drafting, editing, document analysis, message development, copy-paste prompts, and Claude Projects for agency operations.

Related EPR Coverage

• EPR Research Index — every research series in one place
• AI Communications Master Hub — the keystone cluster
• The Citation Share Index — the brand layer companion
• Who Controls AI Answers — the vertical-by-vertical source map
• The GEO Operating Stack — the fourteen-layer operating model
• The AI Communications 100 — the figures shaping the AI answer layer
• AI Communications & GEO: The Practitioner's Guide
• The 50 Subreddits AI Engines Cite Most — the Reddit citation map