# Pin Twilio API and helper-library versions; re-check compliance yearly
Twilio's API surface is unusually stable, which makes agents complacent. The thing that moves is regulation, not the REST paths.
## Procedure
1. The API version is in the URL path: 2010-04-01. Keep it explicit in your code and config rather than relying on SDK defaults you have not read.
2. Pin helper library versions in your lockfile. Twilio ships new SDK majors rarely, but when it does (the v1 to v2 Lookup behavior change is the template: 404 became 200 with valid=false), unpinned upgrades break validation logic silently.
3. Re-check messaging compliance once a year: 10DLC registration rules, toll-free verification requirements, and per-country sender ID rules all tighten over time. Code written against last year's rules can become non-compliant without any code change.
4. When Twilio announces a deprecation or behavior change, treat it as a skill update: write the migration as a checklist (old behavior, new behavior, verification step), not as a code comment.
## Why this matters for agents
An agent's training data freezes at some point in the past. A pinned version plus a dated compliance check turns I think this still works into I verified this works on [date]. That sentence is the whole value proposition of a freshness skill.