PageIndex: Vectorless, Reasoning-based RAG

• [Oct '26] 🔥 Page Search API: find the pages that answer each question in about a second, and send your LLM only those. Cut 97% token cost on document question answering; more accurate and faster than vector search (benchmark).
• [Aug '26] PageIndex SDK: local and cloud modes — one client to index, retrieve, and chat on your machine (with your own LLM API key) or on PageIndex Cloud.
• [Aug '26] ⚡ PageIndex Flash: fast tree index generation for text-based PDFs, now the default indexing method in PageIndex SDK local mode.
• Scale PageIndex to Millions of Documents: PageIndex File System is a file-level tree indexing layer that lets PageIndex reason over an entire corpus, not just a single document.
• PageIndex App: a human-like document analysis agent for long professional documents.

What is PageIndex?

Are you frustrated with vector database retrieval accuracy for long and complex documents? Vector-based RAG retrieves by semantic similarity. But similarity ≠ relevance — what retrieval actually needs is relevance, and relevance requires reasoning. On professional documents that demand contextual understanding, domain expertise, and multi-step reasoning, similarity search misses what is relevant but not similar, and returns what is similar but not relevant.

Inspired by AlphaGo, PageIndex replaces the vector index with a hierarchical tree index and lets an LLM reason its way through it, the way a human expert turns to and reads the right section of a long report. Retrieval happens in two steps:

1. Index: generate a tree-structure index for each document
2. Retrieve: agentically search that tree with LLM reasoning

TL;DR

Compare with Vector RAG

	Vector RAG	PageIndex
Index	vector index	tree index
Retrieval	semantic similarity search	LLM reasoning over the tree
Result	opaque, “vibe retrieval”	traceable to explicit references
Context	query embedding only	full context: conversation history, domain knowledge, etc.

It is ideal for financial reports, legal documents, regulatory filings, technical manuals, medical literature, academic textbooks, and any other long, complex professional document.

Quickstart

pip install -U pageindex

import os
from pageindex import PageIndexClient

os.environ["OPENAI_API_KEY"] = "your-openai-key"

client = PageIndexClient(
    index="gpt-6-luna",                 # model to build the tree index
    chat="gpt-6-sol",                   # model to search the tree
)
doc_id = client.submit_document("report.pdf")["doc_id"]

answer = client.chat("What was the 2023 operating margin?", doc_id=doc_id)
print(answer)

Model Recommendations

• index=: a basic model is sufficient. The tree structure itself is extracted from the document layout without an LLM; the index model only summarizes and refines it, which a basic model does well.
• chat=: use the best model you can afford. The chat model searches the tree to retrieve information. See Query cost and accuracy.

Have a Claude subscription? PageIndex can use your subscription to call Claude models through Claude Code: usage is covered by your plan, no API key needed. Install with pip install -U "pageindex[claude]", then prefix model names with claude-code/, e.g., index="claude-code/haiku", chat="claude-code/opus" (see example).

Use PageIndex through the SDK client →

Configure other models, streaming, multi-document search, citations, and more.

Integrate PageIndex with your own agent →

Drop PageIndex tools into the OpenAI Agents SDK, the Claude Agent SDK, or any other framework.

Benchmarks

Local indexing cost and time

Building a tree locally runs about $0.001 per page with gpt-5.6-luna as the index model, so a 1,000-page textbook costs a little over a dollar and a few minutes, once, and every later question reuses it. PageIndex is designed not to rely heavily on the model used at index time, so in our experiments a basic model does not hurt quality.

Indexing time also scales predictably with document length. In the same local setup, the benchmark documents (9 to 1,098 pages) finished in roughly 13 seconds to 4.5 minutes.

Query cost and accuracy

PageIndex Financial QA Benchmark compares the accuracy and query cost of 34 configurations of 19 LLMs answering 100 questions over 40 Form 10-K filings from 8 companies, with PageIndex doing the retrieval. Cost is measured per 100-question run and excludes one-time indexing.

Full results, data, and reproduction instructions are in the benchmark repo.

Cost per query vs. native PDF input

The alternative to retrieval is handing the model the whole PDF on every question. That cost grows with the document; PageIndex's does not, because it reads only the nodes its reasoning reaches. On documents where both routes return the same answer, native PDF input costs 2.1× more at 52 pages and 16.6× more at 420 (gpt-5.6-sol, prompt caching excluded) — and at 805 pages the document no longer fits in the context window at all.

This is the beginning of the README. Read the rest at the original. Read the full README ↗