Why start with characterisation tests?

They capture what the code does today, so every converted module can be checked against the same behaviour before it merges.

How is a migration priced?

After a fixed-price sample conversion of three to five modules, per module, so the price follows countable units of work.

The upgrade that's been on the roadmap for three years, done module by module

Migration sprints use agents for the bulk of a bounded change (framework and runtime upgrades, test-framework migrations, module extraction, legacy code documented as specs) while engineers review every change. We start with characterisation tests so behaviour is pinned before anything moves, price the work per module after a sample conversion, and track progress module by module.

Book a demo How an engagement runs

Who owns the mistake? The code owners who review each module. Current behaviour is pinned by tests before anything is converted.

Built for CTO · Head of engineering · Engineering manager · Delivery head

The work

How it runs today, and what the agent does instead.

Today

01The upgrade is too big to schedule and too risky to rush.
02End-of-life dates keep arriving and security keeps asking.
03The people who understood the old code have moved on.
04Estimates run to quarters, so it never starts.

With the agent

01InventoryMaps modules, dependencies, test coverage and risk, and picks three to five modules for a sample conversion.
02PinWrites characterisation tests that capture current behaviour before anything changes.
03ConvertAgents convert module by module in small pull requests that pass the pinned tests.
04ReviewA second agent pre-reviews; engineers review every pull request.
05TrackA board of modules: queued, converting, in review, merged, with the long tail called out early.

People decide

Where a person decides. Nothing leaves the building without them.

What comes out

Converted modules merged behind your tests
Characterisation test suite you keep
A per-module price after the sample conversion

Tech leadScope, order and the approach per module.
Code ownersEvery pull request.

The number

We agree the number before we build. Then we report against it every week.

Systems it works in

GitHub
GitLab
Jira
Java, .NET, Node, Python upgrades
Test-framework migrations
Your CI

What we baseline and report on for upgrade and migration sprints
Metric	How it's measured
Modules converted	Merged and passing, per week.
Escaped defects	Regressions found after merge.
Cost per module	Against the original estimate.

Market context

What others are seeing. Their numbers, with their sources. Not ours.

We publish our own numbers for a client only when the client agrees. These are here for context.

4,500
developer-years Amazon estimates it saved on Java upgrades using AI agents.
AWS, 2024(opens in a new tab)
6 weeks
for Airbnb to migrate about 3,500 test files, against an original estimate of a year and a half.
InfoQ, on Airbnb Engineering(opens in a new tab)

Fair questions

What people ask before they trust it.

Our codebase is too old for this.: That's what the sample conversion is for: three to five modules, done for real, before you commit to the rest.
Can you do mainframe or COBOL?: We start where we can prove it: Java, .NET, Node and Python upgrades and test migrations. We'll tell you plainly if your codebase is outside that.

Questions

Upgrade and migration sprints: the short answers.

Also on this desk

Coding-agent rollout and governance Issues in, reviewed releases out For software and technology

Send us ten real documents. We'll show you what an agent does with them.

A one-hour call with a founder and an engineer. Bring a BOQ, a stack of POs, last month's invoices or a backlog, and leave knowing what would work, what wouldn't, and what it would take.

Book a demo or email founders@vegastack.com

170+ projects · 65 companies · founders on every engagement

The upgrade that's been on the roadmap for three years, done module by module

Who owns the mistake? The code owners who review each module. Current behaviour is pinned by tests before anything is converted.

Built for CTO · Head of engineering · Engineering manager · Delivery head

Metric

How it's measured

Modules converted

Merged and passing, per week.

Escaped defects

Regressions found after merge.

Cost per module

Against the original estimate.

The upgrade that's been on the roadmap for three years, done module by module

How it runs today, and what the agent does instead.

Where a person decides. Nothing leaves the building without them.

We agree the number before we build. Then we report against it every week.

What others are seeing. Their numbers, with their sources. Not ours.

What people ask before they trust it.

Upgrade and migration sprints: the short answers.

Why start with characterisation tests?They capture what the code does today, so every converted module can be checked against the same behaviour before it merges.

How is a migration priced?After a fixed-price sample conversion of three to five modules, per module, so the price follows countable units of work.

Send us ten real documents. We'll show you what an agent does with them.

The upgrade that's been on the roadmap for three years, done module by module

How it runs today, and what the agent does instead.

Where a person decides. Nothing leaves the building without them.

We agree the number before we build. Then we report against it every week.

What others are seeing. Their numbers, with their sources. Not ours.

What people ask before they trust it.

Upgrade and migration sprints: the short answers.

Why start with characterisation tests?They capture what the code does today, so every converted module can be checked against the same behaviour before it merges.

How is a migration priced?After a fixed-price sample conversion of three to five modules, per module, so the price follows countable units of work.

Send us ten real documents. We'll show you what an agent does with them.