How it works
Not magic. Bookkeeping.
What the front page showed, opened up: what the model does, what the code guarantees, and how to check it yourself.
§0 · The problem
Three ways to remember, and what each one loses
A summary
A short account, written once.
It goes stale the day it is written, and the correction you made last week is the first thing it smooths away.
Embedding search
Everything, findable by resemblance.
It returns what sounds like your question, not what was decided. It cannot tell a correction from the thing it corrected, or what is current from what was replaced.
A memory file
Facts about you, noted by the model after the fact.
No source to check, no history of how it changed, nothing to undo. It remembers you; it does not know where the work is.
Memory is one layer of context, not the whole of it. Cortex is the layer that decides what context the agent gets, from everything it can read, for the work in front of it. It reads your agent's memory too, as a cross-check, never as the record.
Fig. 1 The loop. A session is compiled once; every later session reads the record, not the transcript.
§1
The loop
- What happens
- A session ends. Cortex compiles what was said into a record. The next session, in any agent, is oriented from that record.
- What is guaranteed
- Your transcripts are read, never rewritten. The record changes only by recorded acts.
- Check it yourself
cortex recap --lastwhat the last session added, each line with its source
§2
Compile: the model reads, the code keeps the books
- What happens
- A language model, yours, reads the finished turns and proposes what matters: decisions, corrections, open questions, where the work stopped. Each proposal is a span of the original words.
- What is guaranteed
- Code checks every proposal before it counts. The words must exist, verbatim, in the turn they cite. What fails is set aside with a named reason, never silently dropped. Nothing is sent to a model without your approval, and a hard cap stops oversized runs.
- Check it yourself
cortex ingest --recent 3 --dry-runthe cost, before anything is sentcortex replay --verifyevery raw record accounted for: kept, or excluded with a reasoncortex droppedwhat was set aside, and why
§3
The record
- What happens
- Units are the words actually said, dated and sourced. States are what those words mean now, each held up by its units, linked to each other. A later correction supersedes a state; it does not erase it.
- What is guaranteed
- No evidence, no state: a state without a source unit cannot exist. Every change is a row in an append-only ledger, and the record's files can be rebuilt from that ledger on any machine.
- Check it yourself
cortex state show <id>a state with its quotes, sources and linkscortex source <session> --message <id>the original turn behind any line
§4
In by default, undone by trail
- What happens
- A change that passes the checks applies at once, made by the compiler, the background daemon or the agent on duty. Changes Cortex is unsure of are flagged, and the next session says so.
- What is guaranteed
- Safety comes from reversibility, not from a queue nobody drains. Every applied change can be inspected and reverted; a revert is itself a recorded act. Destructive changes to a state a person confirmed still wait for a person.
- Check it yourself
cortex patch list --flaggedthe changes Cortex is unsure ofcortex patch revert <id>undo one, by appending its inverse
§5
The read path has no model on it
- What happens
- When an agent needs context, for a goal or for one sentence, Cortex assembles it from the record by fixed rules, within a budget. The agent chooses from what it is given and can ask for more.
- What is guaranteed
- No model decides what you read back: the same record and the same request give the same context, so it can be reproduced and audited. What the budget held back is reported, not hidden. The standing part stays byte-identical across turns, so your provider can cache it.
- Check it yourself
cortex assemble "rotate the stored-card key"the context one sentence gets, and what was held back
§6
The model is rented. The context is yours.
- What happens
- Each agent's transcript format, and each model provider, is an adapter at the edge. The core that compiles and assembles never names a vendor.
- What is guaranteed
- Switching tools changes an adapter, not the record. Change the model, keep the agent: the same one comes back in Claude Code or Codex.
- Check it yourself
cortex config set provider openaipoint compilation at any OpenAI-compatible endpoint, local or hosted
§7
Built like infrastructure
- What happens
- The deterministic kernels run in Rust, kept in step with an independent reference implementation: the whole test suite runs against both, and they must agree. The store lives on your disk.
- What is guaranteed
- Every compiled artifact is signed, and Cortex refuses to load as trusted what carries no valid signature: an edit outside Cortex shows up as tampered. Lapsed licenses never break your own continuity.
- Check it yourself
cortex verify --project <name>check every signature in the store; exits non-zero on tampering
Where it stands
In daily use, building itself and the rest of Arc. Research preview. Core mechanisms patent pending: Arc's patents.
Teams
Shared context across people and machines is coming. The coordination layer will never hold your content.
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