---
type: trekplan-jaccard-calibration
plan_version: "1.7"
created: 2026-05-09
status: parked-synthetic
threshold: 0.55
threshold_basis: "research/02 conservative starting value (arXiv:2412.12148)"
empirical_runs: 0
synthetic_runs: 4
ramp_target: v4.2
---

# Cross-tier Jaccard calibration — voyage v4.1

## Status: PARKED-SYNTHETIC

Empirical Jaccard calibration was deferred from v4.1 because the four
required `/trekplan` invocations cost an estimated $60-120 of LLM-budget
that was not authorized for the v4.1-execute-4b session. Per Step 17
escalate-handler, this file documents:

1. The synthetic placeholder fixtures used by Step 18's smoke-test, and
2. The pinned conservative threshold (`0.55`) from research/02.

## Threshold rationale

`threshold: 0.55` is pinned per research/02 (Recommendation #5):

> "There is no universal Jaccard threshold for cross-model plan
> agreement. arXiv:2412.12148 reports 0.45–0.65 for n=10 task-pair
> samples on coding tasks. We recommend a *conservative starting value
> of 0.55* — this absorbs intra-tier variance and most cross-tier drift,
> while still flagging severe disagreement (e.g. when one tier produces
> a fundamentally different decomposition strategy)."

The 0.55 floor is enforced by `tests/integration/profile-jaccard-smoke.test.mjs`
(Step 18) as a module-local constant `CROSS_TIER_JACCARD_FLOOR`. The test
also gates on a structural pre-check (step-count parity ±20 % and
plan-validator strict pass on both fixtures) — these are *non-negotiable*
even when Jaccard happens to clear 0.55.

## Synthetic fixture pairs

The four parked-synthetic plan-runs in `tests/synthetic/`:

| run-A | run-B | jaccard (synthetic, normalized) |
|-------|-------|---------------------------------|
| profile-plan-run-economy-1.md | profile-plan-run-premium-1.md | 0.707 |
| profile-plan-run-economy-1.md | profile-plan-run-premium-2.md | 0.707 |
| profile-plan-run-economy-2.md | profile-plan-run-premium-1.md | 0.750 |
| profile-plan-run-economy-2.md | profile-plan-run-premium-2.md | 0.750 |

Intra-tier (sanity): economy-1 × economy-2 = 0.935;
premium-1 × premium-2 = 0.905. Intra-tier > cross-tier confirms the
fixtures discriminate.

Min observed cross-tier (synthetic): 0.707. Min minus 0.05 buffer = 0.657.
We pin `threshold: 0.55` — the lower of (research/02 conservative value)
vs (min - 0.05 buffer). This is the same rule plan.md Step 17 prescribes:
`floor(min(jaccard_values), 2) - 0.05` or `0.55`, whichever is lower.

Synthetic Jaccards above are *expected* values for the placeholder
fixtures; real LLM runs will likely differ. The 0.55 pin remains valid
across that uncertainty.

## When to replace these fixtures

Trigger empirical calibration when **any** of the following holds:

1. Cross-tier Jaccard smoke-test (Step 18) flips from green to red on a
   real plan run — indicates the synthetic threshold no longer reflects
   reality and needs re-grounding.
2. v4.2 ROADMAP item "empirical Jaccard calibration" is approved and
   $60-120 LLM-budget is authorized.
3. A new profile is added (`balanced` already exists; if a fourth tier
   like `frontier` is added, recalibrate against premium baseline).

## How to replace

1. Run `/trekplan --profile economy --brief examples/01-add-verbose-flag/brief.md`
   twice. Save each plan's `steps:` frontmatter to
   `profile-plan-run-economy-{1,2}.md` (overwrite synthetic content).
   Update `status: parked-synthetic` → `status: empirical`.
2. Same for `--profile premium`, twice.
3. Recompute the four cross-tier Jaccards. Update the table above.
4. Repin threshold: `min(jaccard_values, 2) - 0.05` or 0.55, whichever
   lower. (Tighter is fine; do not loosen below 0.55.)
5. Run `tests/integration/profile-jaccard-smoke.test.mjs` — must pass.
6. Update `empirical_runs: 4`, `synthetic_runs: 0`,
   `status: empirical`, `ramp_target: stabilized` in this frontmatter.

## Fallback strategy in the meantime

Until real calibration is run, operators are advised to use the
`balanced` profile (sonnet for most phases, opus for plan + review) as
the lowest-risk choice. `balanced` was selected as the v4.1 default in
`commands/trekplan.md` Phase 5.5 specifically to avoid stress-testing
the cross-tier Jaccard floor with parked-synthetic data.