Of the five best-known open-source deep-research agents, one archived itself in August 2026, one rewrote itself into a general agent harness, and one has not taken a commit since September 2025. The research loop became a default feature of every harness, so the only axis left worth choosing on is where your corpus lives and who gets to see the query.
You are not buying retrieval quality from a managed knowledge base — you are buying the connector that copies SharePoint's permissions along with its files, and the query path that enforces them per user. Azure's Agents SDK search tool still cannot forward that token, and permission lock-in is the layer that actually holds you.
A search API returns documents and leaves the agent loop in your process. A research API takes the loop, and that is the trade — you stop paying to orchestrate and you stop being able to instrument. The axis nobody tables is what a citation is: three of these four hand back a bibliography the model assembled, and one binds grounding to a field in a schema you defined, with a confidence. Pick on that, not on report quality.
All four do hybrid search, graphs and agentic retrieval, so the feature table decides nothing. Two things do: whether the framework runs inside your process or arrives as a second production system with its own database, users and on-call — and where the document-parsing boundary sits, because that is what decides whether your best-quality path is open source, a per-page bill, or an integration you own. Pick the posture; the features converged eighteen months ago.
The most-starred open-source text-to-SQL project is read-only — Vanna archived its repo on 29 March 2026 at 23.8k stars — and Dataherald has not taken a commit since July 2024. The two still shipping daily are the two that put a durable, reviewable artefact between the question and the SQL. Frontier models absorbed SQL generation; what they cannot absorb is which of your four definitions of "revenue" this question meant, and that is the layer you own whichever project you pick.
The retrieval quality gap between these four is far smaller than the gap in what an update costs, so the real decision is whether your graph is built once, appended to, or continuously mutated. And all four dedupe entities by string matching, which is the failure nobody's benchmark catches.
Every performance number published about these four engines was written by one of the vendors, and none of them measures the concurrent-write workload agent memory actually generates. What is checkable — licence, write-path concurrency, and whether your memory framework already ships a driver — points somewhere counter-intuitive.
These four price a search between $1 and $16 per thousand, and the spread is not margin — it is how far down the retrieval pipeline each one reads. Price a whole research turn instead of a call and the ordering inverts: the cheapest rate card produces a turn costing three times the dearest one.
A reranker touches no index and holds no state, so swapping one is an afternoon — which finally makes chasing the leaderboard rational, except the leaderboard measures the axis where these four differ least. What differs by more than an order of magnitude is the billing unit and the licence, and both bite hardest at agent scale.
Swapping your LLM edits a prompt. Swapping your embedding model re-embeds the corpus, rebuilds the index and invalidates every retrieval number you have — vectors from two models are not comparable, so there is no gradual migration. That makes this the one choice in a RAG stack you make under lock-in, and the deciding numbers are bytes per vector and who controls the model lifecycle, not a leaderboard rank.
Every document-parser comparison is published as an accuracy leaderboard, and accuracy is the axis that transfers worst to your documents. Two things do transfer: a layout pipeline can drop a number but cannot invent one, and the cost curves of self-hosted and hosted parsing cross at a volume you can compute in five minutes.
List prices for agent search APIs cluster tightly around $5–8 per thousand queries, which makes the sticker the least interesting number in the comparison. What actually differs by an order of magnitude is how many tokens each one dumps into your context per result — and in an agent loop that re-sends its transcript every step, that is the bill.
Before you pick a local vector store, notice that Claude Code, Cursor and Codex deleted theirs — the leading coding agents retrieve with grep, not embeddings. If your corpus still needs an index, these four are not competing products but four different architectures: a search library with no storage, a SQLite extension, an embedded engine with a write-ahead log, and a columnar format on disk.
Four vector stores, four nearly identical feature lists — ANN, filters, hybrid search, all of it. The thing that actually decides which one survives the agentic-RAG stack at scale is invisible there: where the index sits relative to your primary data.