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A steady reading cost, however long the history.

LongMemEval asks questions about long chat histories between a person and an assistant. As the history grew to forty sessions, the reading behind each of MS Duplex’s answers levelled off, and where a fact had changed, it answered with the current one.

LongMemEval, by Wu et al., ICLR 2025. The benchmark →

See it happen →Every result

Internal benchmarks. Every figure on this page comes from tests MatterSpace ran itself and has not been independently verified. Read the disclaimer

  • 96%*Current answers where a fact had changedThe new fact, not the old one
  • 3.7×*Less reading per question than reading the whole historyAt forty sessions of history
  • 84%*Accuracy at forty sessions of history

* Figures from MatterSpace’s internal benchmarks, not independently verified. Read the disclaimer

The history doubles. The reading levels off.

As sessions pile up, the whole history doubles with them.*

Step 1 of 4: The history

3.7× less reading for every answer.*

At forty sessions of history, against sending the whole history to the model.

Step 1 of 3: Reading

MS Duplex sent 24,176 tokens a question. Sending the whole history meant 88,798.*

It answers with the fact as it stands now.

Where a fact changed partway through the history, MS Duplex gave the current answer 96% of the time.*

  • Temporal reasoning: 90% correct.*
  • Reasoning across several sessions: 89% correct.*
Step 1 of 4: Stated

Early in the history, a fact is stated: the team uses vendor A.*

How it was run.

Benchmark
LongMemEval, by Wu et al. (ICLR 2025), from the cleaned public release.
The work
Answer a question about a long chat history between a person and an assistant.
Histories
The sessions holding the answer, mixed with unrelated sessions from a pool of 19,195, at 2, 5, 10, 20 and 40 sessions.
Scale
50 questions at five history sizes: 250 answers for every approach.
Models
GPT-5.5 read what each approach supplied and wrote every answer; a separate model judged them.

What it means for your work.

  • Long-running work stays affordable.

    From twenty to forty sessions the history doubled, and the cost of each answer stayed at $0.032.*

  • Answers follow what changed.

    Where a fact had changed, MS Duplex answered with the current one 96% of the time.*

  • It answers, rather than holding back.

    MS Duplex declined 5 of the 250 questions, and answered the rest.*

Brings the right history to each step →
Next: Blocks every attack, and lets ordinary work through.Read it →

See it on your own work.

From your own assistant to every agent your company runs, a pilot puts MS Duplex on your own work, with the measures agreed before it begins.

Start a pilot →Every result