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Hylen

CAPABILITY · 03 · ENGAGEMENT MODEL

How the work begins. How it ends. What stays behind.

Plain-English engagement terms. Four phases. One audit pack at handover. Your codebase, your CI, your secrets — yours from day one and yours after we leave.

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FOUR PHASES

The arc of an engagement.

Every engagement runs in four phases, on a clock you can plan around. We sign the principles at the start, ship in two-week increments through the middle, and hand over a full audit pack at the close.

  • I
    Frame phase — signed

    Weeks 0 – 2

    FRAME

    Signed engagement letter. Signed operating principles. Architecture sketch on day one. Risk register opened. Audit log started.

    ENGAGEMENT · OPEN
  • II
    Build phase — increments shipped

    Weeks 2 – 10

    BUILD

    Two-week increments. Every sprint ends with shippable code, a signed-off change set, and an updated audit log. Your team can pause us between sprints — no penalty.

    INCREMENT · SHIPPED
  • III
    Validate phase — externally validated

    Weeks 10 – 12

    VALIDATE

    External validation pass. Independent security review. Model cards finalised. Audit pack assembled. Customer counter-sign of the deliverable.

    EXTERNALLY · VALIDATED
  • IV
    Handover phase — keys returned

    Week 12

    HANDOVER

    Codebase signed over. CI under your control. Secrets rotated to your key store. Documentation, runbooks, and the audit pack in your hands. Repository handed over.

    ENGAGEMENT · CLOSED

WHAT YOU LEAVE WITH

Three artefacts. One audit-able engagement.

A handwritten letter on cream paper titled 'REPOSITORY · HANDED OVER' resting on a leather portfolio, with a small USB drive showing a single blue LED on the desk above and a brass key on a navy velvet pouch beside, lit by a brass banker's lamp.

01 · CODEBASE

The codebase, handed over with the keys.

Your repository, your CI, your secrets — from day one. Every commit signed, every release tagged, every secret rotated to your key store at handover. No lock-in, no aftermarket, no vendor key chain.

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A neat stack of cream-paper official reports each marked with a navy 'EXTERNALLY VALIDATED' circular stamp, beside a brass-handled stamp on a desk, a jar of blue sealing-wax beads catching the morning light.

02 · AUDIT PACK

The audit pack — externally validated, sealed.

One bound dossier per engagement. Architecture decisions, security postures, model cards, change set chronology, and an independent validator's seal. Your regulator opens this first — they don't have to ask us anything.

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An antique writing desk lit by a brass banker's lamp — open leather portfolio holding a handwritten 'REPOSITORY · HANDED OVER' letter sealed with a blue wax stamp, a brass key on navy velvet, a single brass coin beside.

03 · KNOWLEDGE TRANSFER

Knowledge transfer — written, recorded, signed off.

Runbooks for every operational scenario. Recorded walkthroughs for every subsystem. Your engineers sign off that they can run it. We stay on retainer for the first 30 days, then we step back unless you want us to stay.

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THE ENGAGEMENT LEDGER

On one side: what you get. On the other: what you sign.

We put both columns on the same page because that's how an honest engagement reads. No surprises in either column. Both sides countersigned before the first sprint.

WHAT YOU GET

  • A working system inside your tenant, on your infrastructure.
  • An audit pack a regulator can open without us in the room.
  • Recorded knowledge transfer for every subsystem we built.
  • Externally validated model cards for every AI component.
  • 30 days of post-handover retainer included — at no charge.
  • An honest answer to every question, in plain English.

countersigned · Hylen Technologies

WHAT YOU SIGN

  • Engagement letter and the twelve operating principles.
  • Master service agreement with the breach-playbook timelines built in.
  • Single-tenant data processing agreement with named subprocessors.
  • Two-person rule policy for production access (your delegates, named).
  • Acceptance certificate at each phase boundary (your team signs).
  • Final handover certificate — repository keys, secrets, audit pack received.

countersigned · customer accountable executive

HOW WE'RE PAID

Fixed-scope, fixed-fee. Sized to the work.

We don't bill by the hour. We don't bill by seat. We agree the scope, the deliverables, and the fee — in writing — before week one. If we miss a milestone, you don't pay for that milestone.

BAND · 01FIXED-SCOPE · FIXED-FEE

PILOT

4–6 weeks · narrow scope · single subsystem · one accountable executive on your side.

LEAVES BEHIND

◆ Working pilot + audit pack

BAND · 02STANDARD · ENGAGEMENT

ENGAGEMENT

10–14 weeks · full operating principles · audit pack + external validation · 30-day retainer included.

LEAVES BEHIND

◆ Production system + sealed audit pack

BAND · 03FIXED-SCOPE · FIXED-FEE

PROGRAMME

Multi-quarter · multiple subsystems · embedded engagement lead · quarterly external validation.

LEAVES BEHIND

◆ Programme audit · quarterly seal

Indicative bands only. Every engagement priced in writing, against scope, before week one.

INSIDE AN ENGAGEMENT

Three moments, three stories.

Anonymised vignettes from the engagements we've run. Each one captures a specific moment in the arc — the day we started, the day we shipped, the day we left.

Three brown leather executive portfolios laid on a long walnut conference table, each opened to a single cream sheet marked with a small blue check mark, a navy ribbon trailing across the middle one, a brass wall clock above showing 14:00.

MOMENT · 01 · FRAME

Day one — three portfolios, one signed line

Three executive teams, one shared sign-off, the engagement letter and operating principles countersigned at 14:00. The clock starts. We don't bill until it ticks.

Read note
A weathered brown leather portfolio on a walnut desk near a window, mounted with a small brass plate reading 'ENGAGEMENT · CLOSED', a wax-sealed cream document peeking beneath, a glass ink jar and a fountain pen on a wooden rest beside it.

MOMENT · 02 · CLOSED

The day the brass plate goes on

Final acceptance signed, audit pack sealed, the brass 'ENGAGEMENT · CLOSED' plate goes on the portfolio cover. We turn the keys over to your team. The retainer clock starts.

Read note
A cream certificate marked 'AUDITED · Q2 · 2026' in navy ink, freshly stamped with a blue wax seal pressed by a brass-handled stamper, a brown leather binder open beside it, soft window light catching the desk edge.

MOMENT · 03 · AUDIT

Audited — Q2 · 2026

External validator drops the seal on the audit pack. Architecture, security posture, model cards, change log — all reviewed by a party with no stake in our reputation. The seal goes on. The pack goes to your regulator.

Read note

ENGAGEMENT · COVENANTS

Four promises we sign before we sign the work order.

Other firms put these in the appendix. We put them in the engagement letter, on the same line as the fee, countersigned by your accountable executive and our engagement lead.

signed, the Hylen covenant
  • Verified

    MILESTONE · NO-HIT-NO-PAY

    Miss a milestone, don't bill for it.

    If we don't ship the milestone on the date we signed against, we don't invoice that milestone. We come back, finish the work, then invoice — never the other way round.

  • Verified

    PAUSE · ON-DEMAND

    Pause us between sprints. No penalty.

    Your team can pause the engagement at any sprint boundary. Notice, not justification. We pick up where we left off when you're ready. No 'continuation fees'.

  • Verified

    REPOSITORY · YOURS

    Your repository, your CI, your secrets — from day one.

    We work inside your environment. Push to your main. Use your CI. Your secret store. Never ours. At handover there's nothing to migrate — only keys to rotate.

  • Verified

    EXIT · CLEAN

    At handover, we leave clean.

    No proprietary frameworks. No lock-in. No 'must call us to upgrade.' Repository signed over, secrets rotated, retainer clock starts, audit pack in your hand.

WHY THIS MATTERS

“An engagement that the customer can't end on a Tuesday isn't an engagement. It's a captive. We sign the exit terms before we sign anything else.”

Operating principle · 12

Hylen

STATUS · OPEN

We have capacity this quarter.

Three new engagements still open before quarter-close. First conversation is on us. We respond within four business hours.