AWS re:Invent 2025

Amazon's Answer to the Productivity Metrics Problem: Cost to Serve Software

原演讲者: Bethany Otto, Technical Program Manager, Amazon Software Builders Experience · Amazon / Eva Knight, Worldwide Go-To-Market Specialist, Next Generation Developer Experience · Amazon Web Services

来源已核验演讲日期待核实presentation41:42EN4 分钟阅读

Individual developer velocity reverts to the team mean, so measuring people measures the team badly — and the only framing that survives a finance conversation is cost per unit delivered rather than time saved.

Amazon's platform team had a good story and the wrong unit. After several years of double-digit improvements to the developer experience, they presented to the executive team and the chief financial officer asked what the company got for it (10:57).

The metrics they had could not answer that question, and the reason is more interesting than the awkwardness of the moment.

Why the obvious answer fails arithmetically

The standard move for a platform team is to add up time saved. A faster build here, a removed manual step there; multiply by engineers, convert to salary cost, present a number.

Bethany Otto explains why they abandoned this, and the objection is not that the figures are soft. It is that they do not compose. Sum the small savings a platform organisation delivers and the total exceeds a hundred per cent of a developer's available time (12:00) — which is a sign the model is wrong, not that the savings are.

Underneath the arithmetic sits a substantive point: a minute returned to a developer is not a minute of code reaching production. Removing friction reduces frustration, which is worth having and is not the same quantity as output. Conflating them produces a number that grows without anything shipping faster.

The alternatives are no better. Lines of code reward verbosity over concision. Time-based measures reward cutting corners and are blind to quality. Per-user telemetry shows what individuals did, which turns out to be the wrong subject entirely (3:22).

The finding that should change how teams are measured

That last point is not an opinion. Amazon analysed indicators of developer success across tens of thousands of engineers over five years, and the result is the most quotable thing in the session.

Individual velocity reverts to the team's mean. A developer with high code-review velocity returns toward the pace of the team they sit in, because that pace is set by the situation — the service's history, its accumulated decisions, the function the team performs (9:13). Team velocity turned out to be the strongest influencer of both individual velocity and perceived productivity (9:35).

If that holds, most individual developer metrics are measuring the team through a person, badly. It also explains why platform work aimed at individuals disappoints: the constraint being optimised was never located there.

Their reframing follows from it. Productivity is an outcome; developer experience is the input. The thing to instrument is the lived daily workflow, not the output count — which sounds soft until you notice it is the only version consistent with the data.

Borrowing a measure from the warehouse

The framework they landed on came from elsewhere in Amazon entirely.

Retail logistics has a measure called cost to serve: what it takes to place a package on a customer's doorstep (12:30). It resists decomposition into individual improvements on purpose. Better picking efficiency, fewer damaged goods, improved demand forecasting — each is a separate intervention, and all of them show up in the same number, because the number describes the system rather than its parts.

Software, they argue, is the same kind of system. The formula they present is deliberately plain: total cost divided by units of delivery (14:42).

The interesting choice is the denominator, which is not fixed. Teams running many microservices use normalised production deployments. Teams shipping a single large application use pull requests. Teams committing to trunk use commits (14:42). The unit fits the delivery model rather than the delivery model bending to the measure — which is what usually goes wrong when a metric is imposed across an organisation.

They are also explicit that velocity alone is not the target. Cost to serve has to move alongside security and resilience, with the cost of maintaining quality sitting inside the numerator rather than outside the frame (15:38). A team that ships faster by shipping worse raises its costs later, and the measure eventually catches it — with a lag they acknowledge rather than hide.

What this is actually for

The framework's value is not precision. It is that it survives contact with a finance conversation.

A platform team armed with time-saved figures is making an argument in a currency the business does not use, which is why the question that started this happened at all. A team that can express improvement as cost per unit delivered is making an argument in the same terms as every other investment the company evaluates.

The cost is that it stops being flattering. Time saved always goes up. Cost to serve can go the wrong way — and when it does, the team finds out that its improvements were absorbed somewhere else in the system. Which is, on the evidence of the sixteen-developer studies circulating this conference season, roughly what has been happening.

关键数据

tens of thousands of developers, 5 years
scale of the analysis showing individual velocity reverts to team mean 9:13
>100%
the total when small time savings are summed, which is why the model breaks 12:00

演讲章节

关键要点

  1. 01

    Lines of code fail as a measure because they reward verbose solutions over concise ones, time-based metrics reward corner-cutting, and per-user telemetry misses what teams actually accomplish. 3:22

  2. 02

    Their framing inverts the usual one: productivity is the outcome, developer experience is the input, so the thing to instrument is the lived daily workflow rather than the output count. 4:17

  3. 03

    An analysis spanning tens of thousands of developers over five years found individual velocity reverts to the team's mean — the empirical argument against measuring individuals. 9:13

  4. 04

    Team velocity emerged as the strongest influencer of both individual velocity and perceived productivity, which is why their platform work targets teams rather than people. 9:35

  5. 05

    The trigger for the whole framework was a finance question their existing metrics could not answer — what the company actually gets for the improvement. 10:57

  6. 06

    Summing small time savings breaks down arithmetically: the total exceeds a hundred per cent of available time, and a minute returned to a developer does not become code in production. 12:00

  7. 07

    Cost to serve software borrows directly from Amazon's retail supply chain measure of what it costs to place a package on a customer's doorstep, applied to a system that is equally complex. 12:30

  8. 08

    The formula is total cost divided by units of delivery, where the unit is chosen per team — normalised production deployments for microservices, pull requests, or commits to trunk. 14:42

  9. 09

    They are explicit that velocity alone is insufficient: cost to serve must move in tandem with security and resilience, with quality costs sitting inside the numerator. 15:38

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