Boundary ML

BAML's argument is that agent-written software changes the tradeoff TypeScript made. TypeScript deliberately allows unsoundness and escape hatches because that helped humans ship web apps; an agent will eventually use every escape hatch you leave open. BAML's answer is to make invalid states difficult to represent, keep changes local, expose nondeterminism, and give agents structured ways to inspect a codebase. That last part is what separates it from a schema library — `baml describe` gives an editing agent AST-aware discovery of your project, and `baml agent install` installs guidance matched to the BAML version you have pinned, so the agent's instructions don't drift from your toolchain.On the practical side, the language itself is unremarkable in the best way: TypeScript-like syntax, unions, generics and interfaces, runtime-checked types, typed errors with exhaustive pattern matching. The runtime plumbing you'd otherwise hand-roll is in the stdlib — retry, fallback, round-robin and streaming clients — plus green threads via `spawn` and `await` for concurrency. Tests, testsets and evaluations are first-class rather than bolted on, and `baml test` runs them in CI, which is where prompt regression drift actually gets caught. SDK generation for Python and TypeScript means you adopt it inside an existing app rather than rewriting it.The October 8, 2026 release (0.21.0) is the most substantive recent step: SQL queries over recorded runs, per-call tracing, regex, structural map keys and Bedrock streaming. Cloud is explicitly not required to run BAML locally, so the local toolchain stands on its own, but teams that need hosted governance today can't buy it yet.Where it fits: extraction and classification pipelines over unstructured text (resumes, invoices, support tickets), agents that need typed intents and entities, and multi-service shops that want one schema enforced across Python and TypeScript. Where it doesn't: low-code teams who want a visual builder, and teams allergic to pre-1.0 churn — 0.21.0 lists migrations needed to upgrade, and there have been five releases between 0.17.0 in mid-August and 0.21.0 in October 2026. Install instructions shown target macOS and Linux via Homebrew or the install script. That's a fast-moving project, and the price of admission is tracking it.