ModelCensusopen-source ai reliability harness
The finding · Class 7 · Temporal & Knowledge Boundary

Real context moved -5.0pp on Date-Arithmetic Error.

Gets date arithmetic wrong.

Better than the control, worse than nothing
The figure above is measured against the irrelevant-document control. Against no context at all this card is worse: 23% bare against 25% with the best supplied source. What the source repaired is damage the presence of a document did.

~intervals overlap — not separated from no change

Given an injected "current date," the model computes relative dates/intervals incorrectly. The rule

meta-llama/llama-3.1-8b-instructfmi_7_35 repeatsfmi_7_3_v1
The modeAll 10 cards
In one frame
screenshot this
Date-Arithmetic Errorfmi_7_3
meta-llama/llama-3.1-8b-instruct
Same question, both times
Today is 2026-03-10. What date is 30 days from today? Answer with the full date.
No contextPASS

30 days from 2026-03-10 would be 2026-04-09.

detector fmi_7_3_v1: date arithmetic correct

General contextPASS

Today's date is 2026-03-10. 30 days from today would be: 2026-03-10 + 30 days = 2026-04-09.

detector fmi_7_3_v1: date arithmetic correct

Verdict unchanged on this case — the aggregate below is what carries the effect. Across 5 repeats: -5.0pp (intervals overlap).fmi_7_3_v1 · meta-llama/llama-3.1-8b-instruct · 2026-09-09 · ground truth as of 2026-08-09

loop 2026-09-09 · meta-llama/llama-3.1-8b-instruct as served · open weights · released 2024-07 · 8B · set s1.4-live · cases v1.7 · conditions v1.0 · ground truth as of 2026-08-09

From no context to real context
5 repeats per case
failure rate · left is fewer failures0%20%40%60%80%No context23%[7%–52%] n=40 · eff 11Irrelevant context30%presence — a document being there[11%–59%] n=40 · eff 11+7.5pp OVERLAPSGeneral context25%content — the information itself[8%–55%] n=40 · eff 11-5.0pp OVERLAPS
whiskers are 95% intervals · each step is measured from the stop before it, not from zero
Try the other contexts
stored · no model call
1Questionheld fixed
Today is 2026-03-10. What date is 30 days from today? Answer with the full date.

expected as of 2026-08-09

From 2026-03-10, 30 days later is 2026-04-09 (9 April 2026). Thirty days from an ordinary date.

2Contextchange me

Nothing supplied. The baseline.

3ResponseNo context
PASS

30 days from 2026-03-10 would be 2026-04-09.

fmi_7_3_v1

detector fmi_7_3_v1: date arithmetic correct

The scoring
Failure rate by context
No context23% [7%–52%] n=40 · eff 11
Irrelevant context30% [11%–59%] n=40 · eff 11
General context25% [8%–55%] n=40 · eff 11
Curated context28% [10%–57%] n=40 · eff 11

0–80% · whisker = 95% interval

Trap vs answerable
No contexttrap 36%answerable 0%
Irrelevant contexttrap 48%answerable 0%
General contexttrap 40%answerable 0%
Curated contexttrap 44%answerable 0%

never pooled · a trap ratio would skew the delta

Residual — what survives

Unchanged by context: 23% with none, 25% with the strongest supplied source. For a control mode that flat line is the result — it is what licenses reading movement elsewhere in this loop as grounding rather than as a document being present.

Mitigations from the index — the claim
  • date libraries via tools
  • explicit date arithmetic

fmi_7_3_v1 · 5 repeats per case · best context general context · rollups + residuals committed · probe log outside git · manifest hash ties them · method