Don’t switch AI models blind. See what breaks first.
Hajer gives engineering leaders an independent assessment of one production model migration. We compare a candidate with the behavior your system already depends on and produce a traceable record of what held, what changed, and what the evidence cannot determine.
Your team keeps the final release decision.
Founder-led assessments for technical teams evaluating a real model change.
Requests move left to right. Hajer marks concerning changes in orange and removes them from the candidate stream while consistent behavior continues. This illustrates assessment—not runtime enforcement or a customer result.
The API can keep working while your product quietly changes.
Replacing an AI model is not the same as upgrading an ordinary software dependency. The candidate may return valid, convincing responses while changing behavior your customers, workflows, or business rules depend on.
Traditional tests may confirm that the request succeeds, the schema is valid, and the service remains online. They may not reveal that instructions are interpreted differently, tool arguments move, refusals shift, or the business outcome changes.
The easy question
“Does the new model work?”
The decision-bearing question
“What changed in our actual system, does it matter, and is the available evidence strong enough to support proceeding?”
See what breaks.
A replacement can return polished, valid responses while changing behavior the product depends on. Choose a pattern to compare the current and candidate behavior.
Illustrative change
Tool argument drift
Numbers become strings, optional fields disappear, enum casing changes, or dates use a different format even though the tool call still validates.
The request succeeds at the model boundary. The break appears later when application logic depends on the missing or changed value.
These are illustrative patterns, not customer results. A real assessment stays bounded to the customer’s workflow, evidence, and agreed conditions.
A focused assessment for one model change.
Hajer keeps the engagement tied to one concrete production decision and the evidence available for it.
The engagement stays bounded
- 01One agreed migration scope
- 02The production behavior your team depends on
- 03Observed changes in the candidate
- 04Limitations in the available evidence
Hajer will not rank every model, choose the customer’s provider, certify a system as safe, or authorize a release.
What you receive
A clear record for the decision in front of you.
Each assessment stays tied to one agreed migration scope.
Scoped findings
A focused account of the agreed migration scope.
Observed changes
A clear record of what changed and what remained consistent.
Explicit limitations
What the available evidence could not determine.
Recommended next action
The next step supported by the findings and remaining uncertainty.
Your team retains authority over model choice, deployment, and release.
A traceable decision record—not “Model B won.”
The decision record gives the engineering owner a clear account of the migration, with every conclusion tied to the evidence and limitations behind it.
A responsible conclusion may support proceeding, require further review, identify a blocker, or state that the evidence is insufficient. Uncertainty is not converted into a passing score.
Decision record
- 01What was assessed
- 02Which baseline and candidate configurations were used
- 03What evidence was available—and what it represented
- 04What remained consistent
- 05What materially changed
- 06Which agreed conditions were satisfied or violated
- 07What could not be determined
- 08What should happen next
For engineering owners
Built for one consequential model change.
Hajer is for technical founders, CTOs, and engineering leaders who own a production model change and need a defensible basis for the decision.
The engagement stays narrow
- One production workflow
- One accepted baseline
- One candidate configuration
- One traceable decision record
Strongest fit
- An AI workflow already runs in production
- A model change has become a real engineering decision
- An accountable technical owner keeps release authority
- Authorized workflow evidence is available for assessment
Start with the migration
Tell us which model change your team is evaluating, why it matters, and what evidence exists in the workflow today.
Questions engineering leaders ask first.
Bring us the model change your team needs to defend.
We want to speak with technical founders, CTOs, and engineering leaders evaluating a real AI-system change—whether driven by cost, latency, capability, provider availability, or product requirements.
Assessments are scoped directly with the engineering owner responsible for the change.