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.
The same product has been reported at 49.0% and at 94.4% on a benchmark with the same name, depending on who ran it and when. Scores cannot arbitrate this category. What actually differs between the four — and what you cannot change after adoption — is who decides what gets remembered, who invalidates it, and whether you can get it back out.
A 128K-token context window degrades past the first thousand tokens and vanishes the moment the session ends. The agent-memory infrastructure market crossed $6 billion in 2026 because "throw it all in the context" stopped being a strategy — and four frameworks now bet differently on what memory should rank, store, and forget.
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