ModelCensusopen-source ai reliability harness
The finding · Class 4 · Reasoning & Calculation

Real context moved 0.0pp on Dimensional-Analysis Failure.

~intervals overlap — not separated from no change

The model produces a quantity with inconsistent or wrong units, or mixes unit systems, yielding a dimensionally invalid result. The rule

anthropic/claude-sonnet-4.6fmi_4_45 repeatsfmi_4_4_v1
The modeAll 10 cards
In one frame
screenshot this
Dimensional-Analysis Failurefmi_4_4
anthropic/claude-sonnet-4.6
Same question, both times
A tank fills at 3 L/min for 4 minutes, then drains at 500 mL/s for 10 seconds. Net litres?
No contextPASS

## Setting Up the Problem ### Filling Phase - Rate: 3 L/min - Time: 4 minutes - Volume added: 3 L/min × 4 min = **12 L** ### Draining Phase - Rate: 500 mL/s = 0.5 L/s - Time: 10 seconds - Volume removed: 0.5 L/s × 10 s = **5 L** ### Net Volume Net = 12 L − 5 L = **7 L** Answer: 7 L

detector fmi_4_4_v1: correct unit L

General contextPASS

## Setting Up the Problem **Filling phase:** - Rate: 3 L/min - Time: 4 minutes - Volume added: 3 × 4 = **12 L** **Draining phase:** - Rate: 500 mL/s = 0.5 L/s - Time: 10 seconds - Volume removed: 0.5 × 10 = **5 L** ## Net Volume Net = 12 L − 5 L = **7 L** Answer: 7 L

detector fmi_4_4_v1: correct unit L

Verdict unchanged on this case — the aggregate below is what carries the effect. Across 5 repeats: 0.0pp (intervals overlap).fmi_4_4_v1 · anthropic/claude-sonnet-4.6 · 2026-08-15 · ground truth as of 2026-08-09

loop 2026-08-15 · anthropic/claude-sonnet-4.6 as served · closed weights · released 2026-02 · set s1.3-live · cases v1.6 · 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%5%10%15%20%No context0%[0%–7%] n=50Irrelevant context0%presence — a document being there[0%–7%] n=500.0pp OVERLAPSGeneral context0%content — the information itself[0%–7%] n=500.0pp 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
A tank fills at 3 L/min for 4 minutes, then drains at 500 mL/s for 10 seconds. Net litres?

expected as of 2026-08-09

12 L in, 5 L out, net 7 L. The mixed units are the trap.

2Contextchange me

Nothing supplied. The baseline.

3ResponseNo context
PASS

## Setting Up the Problem ### Filling Phase - Rate: 3 L/min - Time: 4 minutes - Volume added: 3 L/min × 4 min = **12 L** ### Draining Phase - Rate: 500 mL/s = 0.5 L/s - Time: 10 seconds - Volume removed: 0.5 L/s × 10 s = **5 L** ### Net Volume Net = 12 L − 5 L = **7 L** Answer: 7 L

fmi_4_4_v1

detector fmi_4_4_v1: correct unit L

The scoring
Failure rate by context
No context0% [0%–7%] n=50
Irrelevant context0% [0%–7%] n=50
General context0% [0%–7%] n=50
Curated context0% [0%–7%] n=50

0–20% · whisker = 95% interval

Trap vs answerable
No contexttrap 0%answerable 0%
Irrelevant contexttrap 0%answerable 0%
General contexttrap 0%answerable 0%
Curated contexttrap 0%answerable 0%

never pooled · a trap ratio would skew the delta

Residual — what survives

Unchanged by context: 0% with none, 0% 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. Nothing survives at the best condition on the cases measured here.

Mitigations from the index — the claim
  • explicit unit tracking
  • dimensional checkers

fmi_4_4_v1 · 5 repeats per case · best context general context · rollups + residuals committed · probe log outside git · manifest hash ties them · method