What trunk-based development actually demands, not what it promises
The pitch for trunk-based development usually stops at "everyone commits to main, all the time." That's the mechanic, not the requirement. What it actually demands is that the main is always deployable, by anyone, at any moment, without a human checking first. That's a much bigger ask than it sounds. It means your test suite has to catch real regressions, not just run. It means a broken build gets fixed in minutes, not by the end of the day. It means incomplete work has to live in production code without being visible to users, which is a different skill than writing correct code. Teams hear "trunk-based development" and picture a git workflow. It's actually an operating model for the whole delivery pipeline, and the git workflow is the last piece, not the first.
The CI pipeline is the first thing that breaks
Feature branches hide a lot of sins. A CI pipeline that takes forty minutes is annoying on a branch, but it's tolerable because you're not blocking anyone else. Move to trunk-based development, and that same forty-minute pipeline becomes a queue. Five people push in an hour, and now the fifth person's change isn't validated until everyone ahead of them clears the pipeline. If any of those four break the build, the fifth person inherits the mess. Teams that migrate without addressing pipeline speed end up with a main branch that's red more often than green, which defeats the entire point. The fix isn't glamorous: parallelized test execution, a fast smoke-test tier that runs on every commit with the full suite running less frequently, and a hard rule that a red build gets fixed before anything else happens. If your CI pipeline can't get a commit from push to "safe to build on" in under ten minutes, trunk-based development will make your team slower, not faster.
There's a middle path most teams skip past: partial adoption. You don't need every service on trunk-based development on day one. Pick the service with the best test coverage and the simplest deploy story, run trunk-based development there for a quarter, and use what breaks as the punch list for every other team before they migrate. Teams that try to flip the whole organization at once inherit every gap simultaneously, across every codebase, with no isolated place to learn the failure modes before they get expensive.
Feature flags are not optional; they're the whole mechanism
Here's the part that trips up teams the most: without feature flags, trunk-based development just means constantly shipping half-finished work to production. That's not a workflow improvement; it's a liability. Feature flags are what let you merge incomplete work into main without exposing it, which is the actual trick that makes small, frequent merges possible. But flags have a cost most teams underestimate. Every flag is a branch in your code that has to be tested, and flags that live for months because nobody cleans them up turn your codebase into a maze of conditional logic nobody trusts. Teams that do this well treat flag creation and removal as equally important steps in the same workflow, with an owner and an expiration date assigned to every flag at creation. Teams that do it poorly end up with three overlapping flags controlling the same feature, and no one is sure which one actually matters in production. If your team doesn't already have a lightweight way to gate code behind a flag and a discipline for retiring them, that's a gap to close before trunk-based development, not during it.
Test coverage has to replace the safety net code review that used to be
In a long-lived branch workflow, a large pull request serves as a checkpoint. A reviewer reads fifteen files, thinks about the interactions, and catches things a compiler won't. Trunk-based development compresses changes into small, frequent commits, which helps reduce merge pain, but it also shrinks each review to the point where it can't catch systemic issues anymore. Nobody's going to spot a subtle race condition in a twelve-line diff if the twelve lines look correct in isolation. That job has to move somewhere, and the only place it can move is automated tests: integration tests that exercise real interactions between components, and enough of them that a change that breaks something downstream fails loudly before it reaches main. Teams with thin test coverage that adopt trunk-based development usually don't notice the gap until production, because the thing that used to catch these problems (a human reading a large diff) is gone, and nothing has replaced it.
Trunk-based development punishes weak ownership habits immediately
There's a cultural precondition that's harder to measure than pipeline speed or test coverage, and it's the one teams skip past. Trunk-based development only works if a broken build is treated as the team's most urgent problem, ahead of whatever anyone was working on individually. That sounds obvious written down. In practice, it means the engineer who broke the build stops what they're doing and fixes it, and everyone else either helps or waits, because building on top of a broken main compounds the problem for every subsequent commit. Teams with a habit of "I'll look at it after lunch" or "it's probably not my change" don't survive this. The failure mode isn't dramatic; it's just main staying red for hours at a time, which quietly erodes the one property that makes trunk-based development worth doing in the first place: that main is always safe to build on.
Signs your team is actually ready, not just excited
A few concrete signals matter more than enthusiasm. If your CI pipeline consistently finishes in single-digit minutes, that's a real signal. If your team already uses feature flags for something, even imperfectly, that's a real signal, because it means the muscle exists. If a broken build gets attention within minutes without someone having to escalate it, that's a real signal, because it means the ownership culture is already there. If your test suite has caught a real regression in the last month before it hit production, that's a real signal, because it means the tests are doing actual work, not just passing. None of these need to be perfect. But if none of them are true yet, the honest move is to fix them first, under whatever branching model you're using today, and revisit trunk-based development once they are.
Why rushing this costs more than staying on branches
The sequencing matters more than the enthusiasm. Fix CI speed first, because everything else is measured in minutes you don't have if the pipeline is slow. Build feature-flag discipline second, because retrofitting flag hygiene into a codebase that’s already been migrated is far harder than building it in from the start. Raise test coverage on the critical paths third, since that piece takes the longest and benefits the most from not being rushed. Trunk-based development itself is the last domino, not the first.
