Codex project memory: cost benchmarks

On 23 September 2026, Codex with Pairon’s project memory solved the same pinned tasks for less than Codex alone. Cost per successful answer was 33% lower on Simulation 1, 22% lower on Simulation 2, and 19% lower on Simulation 3.

The run was Codex · gpt-5.6-luna · low effort, 360 paired runs. Every 90% confidence interval for those ratios was below 1. No significant difference in hand-graded answer quality on any set. Cost uses the harness’s fixed notional token prices, the same for both arms, not what Codex bills.

Source: Pairon-Backend docs/benchmarks.md, report BENCHMARK-2026-09-23-v3-codex-luna-low.md, dated 2026-09-23.

The shared context guide explains what project memory is for. The Codex team workflow shows how to use the agent in a shared room.

• Simulation 1. Ratio 0.674 (33% lower cost per success). 90% CI 0.538–0.835.
• Simulation 2. Ratio 0.778 (22% lower cost per success). 90% CI 0.619–0.944.
• Simulation 3. Ratio 0.811 (19% lower cost per success). 90% CI 0.702–0.936.

One of the three repositories is not maintained by Pairon, so the result does not rest only on Pairon’s own code.

• Two identical copies. Each task runs on a plain checkout and on a Pairon checkout of the same pinned commit. Both reset before every run, and the arm order alternates.
• Answers stay hidden. Benchmark material is excluded from both copies, so neither agent can read the expected answer.
• People grade the work. Every automatic failure and a sample of passes are checked by hand: cited lines, completeness, exact locations, clean edits.
• Cost per success. Total cost divided by the answers that passed grading, so a cheap wrong answer never counts as a saving.

Ratio means cost per successful answer with Pairon, divided by cost per successful answer without it. A number below 1 is a saving. A cheap wrong answer does not count as one.

These were measured on Codex and left off by default. Publishing only the memory result would hide them.

• Hand-off package. Ratio 0.97 [0.87, 1.09]. Its facts were change notes rather than how the code works. Opt-in only.
• Procedures. −14%, +20%, +14%. Missed the −30% target and stayed within run-to-run noise. Opt-in only.
• Output compressor. +3%, +33%, +80%. On the three valid pairs; the test output here was too small to compress. Off by default.
• pairon_ask tool. +10% cost. Codex never called it. No value on Codex.

• One agent (Codex) and one model at low effort. Claude Code and OpenCode were not part of this run.
• 60 paired tasks per repository bound cost well, but answer quality only to about ±10 points.
• This measures one agent using Pairon’s project memory. It does not measure teams.

The team calculator on the homepage is a simulation. It is labelled as one. It is not this benchmark. How it works describes the product the measurement belongs to.