Prise the assumptions out of the cells they hide in, give each one an owner and a date, and rank the handful that actually move the answer before anyone argues the central case.
A case is built, and every assumption inside it is lifted out of the formula and named.
02
An assumption changes, and the owner who set it and the date they set it move with it.
Reason
03
A range of cases opens, and not one is labelled expected, because a case is not a forecast.
04
A sensitivity run finishes, and the drivers that move the answer most are ranked before it is read.
05
A pair of drivers moves together, and neither may be flexed as though the other stood still.
Decide
06
An input goes stale, and the case resting on it is marked stale rather than quietly carried on.
07
A model is reopened a year later, and its version, provenance and purpose note are still attached.
Out
08
A plan is chosen, and that choice belongs to finance and the people accountable for it.
09
Execute write actions only inside the approval boundaries agreed during implementation.
→Product statement
Case building and sensitivity ranking belong to the agent. A named owner sets each assumption, and finance owns the plan chosen from the cases.
Example workflow
One case, assumption to publication
AgentHuman
1Planning inputs receivedBudget models, driver files, actuals extracts or the planning system itself
2Case context assembledThe decision under test, the drivers it turns on, the sources behind them and the day each was refreshed
3Assumption register draftedThe assumption, its owner, its source and the range it may travel
4Controls appliedCorrelation checks, freshness checks, range checks and visibility confidence
No human action required
Stages 1 to 4 run unaided, and no plan is chosen at any of them — the agent only models, and the finance partner enters at the visibility gate.
5DecisionSplits at the visibility gate
Assumptions all owned
Passes to the finance partner for release.
Anything unowned
Adds a planning analyst read first.
Planning review
The case is held with its register, its gaps and the owners still to confirm.
Publish · Append assumption · Send to planning review
Published — by the finance partner▼
6Planning and model records updatedOnly where write access and records policy allow it
7Outcome evaluatedAssumption visibility, sensitivity coverage, analyst corrections and what review found
Corrections
Each analyst correction is counted in the evaluation.
What should not run autonomously
Human approval stays in control
Outside the boundary — human approval required8 items
Choosing which case becomes the plan.
Setting the value an assumption is modelled at.
Declaring any case the expected outcome.
Signing off a planning round for finance.
Automation boundaryAgent acts unaided
✓Lift each assumption out of the formulas into a named register.
✓Rank the drivers by the distance each one moves.
✓Flag the driver pairs that move together, never apart.
✓Mark a case stale the moment its source data stops being current.
No case is published and no plan is ever chosen except by a named person, on approval.
Judging which of the cases is the likelier one.
Telling the board that a scenario will happen.
Owning an assumption on behalf of a person.
Changes to the model, the register or the plan.
Example output
One assumption, annotated
This serves a strategy team whose model gets reopened by somebody else in a later planning round, so the owner, the version and the purpose note travel with every case.
Assumption record · single caseIllustrative example
Assumption
Recorded as
Case
Evidence of record
Confidence
Held for
Revenue growth rate, base driver
Set by the named owner, sourced and dated
Downside case
Planning driver file, 3 August 2026
Held unpublished
The finance partner, by name
As receivedSourced from the driver file and the planning system — nothing behind those two shows here.
What the record holdsDriver fileAssumption owner notePrior-round model
Why nothing is predicted hereWhich case actually occurs is not something this model claims to know.
ActionPublishAppend assumptionSend to planning review
What the score decidesBelow the configured threshold a case picks up a planning read before the partner sees it.
Value
Where AI adds value
The same four claims, placed at the point in the workflow where each one applies.
Where the value landsValue 01 – 04
Every assumptionFrom the owner who set it
03Evidence
Where the evidence is used
A scenario is not a forecast: this page shows the cases built and the assumptions under each, and it makes no claim about which of them will happen.
01Approved path
An assumption is a choice
Somebody chose that growth rate, and the register carries their name and the day beside it, not the formula on its own.
02Human review
What was checked, and not found
No published benchmark exists for how often a planning assumption survives the round it was set in, so none is quoted here; and how any case compared with the year that followed is not something this page claims to know.
04Build an evidence trail
The scenario, the assumption driving it and the owner who set it stay together.
Integrations
Typical integrations
Five system groups connect to the same agent. Which of them are in scope is decided in discovery.
Planning and budgetingPlanning system · budget models Driver files and case versions
Finance and actualsGeneral ledger · close reporting Actuals and variance history
Commercial and operationsPipeline · capacity · pricing Volume, price and cost drivers
Agent
Scenario and sensitivity modelling
Reads the drivers Builds the cases Holds for the partner
Market and external inputsIndex feeds · research files Rate, index and demand assumptions
A scenario-level assumption-visibility figure can read clean while multi-year strategic cases carry most of the rework. Nestack reports the correction rate by case type, not only in total.
Slice performance — reported separately, not only in aggregateIllustrative example
Slice
Failure rate
Lift
Lift vs. threshold
Status
Multi-year strategic cases
8.3%
3.6×
Review
Annual plan cases
5.9%
2.6×
Review
Quarterly reforecast cases
3.7%
1.6×
Watch
Steady-state base cases
1.5%
0.7×
Normal
Bar: correction-rate lift vs. steady-state base-case baseline · scale 0–4.0× · tick marks the 2.0× review threshold2 of 4 slices over threshold
Evidence-linked improvement
What a buried assumption costs
A cycle ends when the buried assumption is a standing case. That suite is what the next model published is measured against.
Improvement cycle · five stagesSwitchback — the path turns at Improve and returns at Learn
01Detect
Correction rate rises on multi-year strategic cases.
02Diagnose
The growth rate buried in a cell that three quarters of planning rested on is traced back until one cause is left standing.
03Improve
Changes leave numbered, and the scenarios that forced them travel attached.
04Verify
One scenario case still failing is enough to stop the whole release.
05Learn
The case is kept, and the assumption rules are rewritten alongside it.
Learn → DetectThe return edge. The next case is measured against a suite one case longer.
Typical build scope
Twelve workstreams across six weeks
The build scope read against the delivery timeline. Week structure follows the six-week plan — discovery, sources, case assembly, evaluation, integration, then production validation and handover.
WorkstreamWeek 1Week 2Week 3Week 4Week 5Week 6
01Assumption-register and automation-boundary work.
02Planning, ledger and market sources.
03Assumption-to-owner and sensitivity-coverage mapping.
04Driver and actuals ingestion.
05Assumption, owner and source binding.
06Visibility scoring and review routing.
07Finance partner release workflow.
08Planning-system integration.
09Assumption and sensitivity cases.
10Guardrails and publication controls.
11Scenario-trail instrumentation.
12Deployment, documentation and Agent Care handover.
12 workstreams · 6 weeks · bar shows the weeks a workstream is active — several run in parallelFinal scope and sequence confirmed in discovery
Engagement tiers
What each tier includes
Rows are the capabilities named in each tier's scope. Higher tiers include everything below them.
Capability✓ in scope · — not at this tierPilotOne round, one modelProductionProduction planning workflowAdvancedMultiple rounds / entities
Introduced at Pilot
Case assembly to your drivers✓✓✓
Finance partner release✓✓✓
Assumption-register baseline✓✓✓
Introduced at Production
Reporting by scenario—✓✓
Partner sign-off workflow in your systems—✓✓
Approved write-back—✓✓
Planning-model integration—✓✓
Introduced at Advanced
Multi-entity plans——✓
Cross-round case packs——✓
Large driver estates——✓
Multi-case version controls——✓
Build priceFrom $5,000From $8,000Custom quote
Final build priceConfirmed after discovery based on integrations, workflow complexity, model size, approval controls and deployment requirements.
Separate from buildBuild pricing is separate from recurring Agent Care, which covers managed monitoring, evaluations, incidents and verified improvements after launch.
What we need from you
What you bring, and what we build with it
Each input maps to a piece of build scope and a week in the delivery timeline.
You bringWe build with it
01Your planning model and the drivers it turns on→Driver mapping and assumption captureWeek 1
02Representative planning, actuals and market inputs→Source binding, assumption logic and the register baselineWeek 2
03Your planning calendar and the owners it names→Driver mapping, owner binding and the automation boundaryWeek 1
04Access to relevant APIs, feeds or exports→Planning, ledger and market source assessment, then integration setupWeek 2
05Models you would not want opened→Sensitivity cases and the evaluation suiteWeek 4
06What no scenario model may predict→Visibility scoring, review routing, guardrails and release controlsWeek 3
07A finance partner who owns the plan→Release to the finance partner, then pilot and production validationWeeks 5–6
Nothing else is requiredDeployment, documentation and Agent Care handover are ours.
Delivery timeline
Four phases across six weeks
The fifth week doubles because two phases really do run together, not because the row needed filling.
PhaseW1W2W3W4W5W6
DiscoveryW1
BuildW2 – W3
EvaluateW4 – W5
Pilot & LaunchW5 – W6
Week focusW1Planning workflow discovery, driver mapping and the automation boundaryW2Source integration and the assumption-register baselineW3Case assembly, sensitivity logic and release controlsW4Evaluation suite, sensitivity cases and failure-mode testingW5Planning-system integration, pilot cases and targeted correctionsW6One planning round run under the finance partner, then Agent Care handover
Reading the bandEach bar covers only the weeks its own work is named for, and week five holds a pair that genuinely overlap.
At the end of W6When the assumption record validates, Agent Care picks the agent up.
DurationSix-week plan shown · typical delivery 4–6 weeks depending on scope confirmed in discovery.
Next step · Strategy AI agent
Build a scenario agent on the assumptions your planning model keeps out of sight.
Show us one case and the assumptions under it. If the model that sets your plan cannot be reopened next year without its author sitting beside it, then it costs a rebuild every round. Choosing the plan stays with finance; the agent builds cases and ranks what moves them.
