Is Bend 2 free to use?

Bend 2 is Apache-2.0 licensed and developed in the open at github.com/bendlang/bend, so it is free for commercial and personal work. Installation is a single shell command from bend-lang.com, and the repository ships the compiler, the guide and the proof checker together rather than splitting a paid tier out of the toolchain.

Do Bend 1 programs still run on Bend 2?

No. The Bend project states that Bend 1 programs do not carry forward to Bend 2, so existing code has to be rewritten rather than migrated. Bend 1 was a massively parallel functional language; Bend 2 keeps the parallel execution story but rebuilds the language around dependent types and checked program laws, which is why compatibility was dropped.

What can Bend 2 not do yet?

The Bend 2 repository lists its own limits plainly: no type inference, no macros, no separate compilation, no multi-machine execution, no Windows support, and only three numeric types — Nat, U32 and F32. Native compilation is also described as slow. These are documented gaps rather than bugs, so early users should expect to write more type annotations than usual.

How much of the Bend 2 compiler was written by AI?

The Bend repository says the compiler is 99% AI-written and has not been fully audited yet. That is an unusual disclosure for a tool whose selling point is mechanical trust, and it is the main caveat for anyone considering Bend 2 for safety-relevant code: the proof checker's own implementation has not had the human review that its output is meant to replace.

How fast is Bend 2 at checking proofs?

Bend's project page claims its proof checker beats other proof assistants by several orders of magnitude, verifying proofs in under a second where competing tools take minutes. Those are the project's own published figures rather than independent measurements, and the repository also claims C-level speed on CPUs and CUDA-level throughput on GPUs for ordinary programs.

Bend · 2026-09-17 · major

Bend 2 — a language that makes an AI prove its code obeys your laws

Bend 2 went public on 17 September 2026. You write rules in a LAWS.bend file and the compiler rejects any edit it cannot prove keeps them, which is aimed at AI-written code. It compiles to C, Metal, CUDA and JavaScript.

GitHub social card for the bendlang/bend repository

Declare the rules your program must never break, and Bend 2 refuses to compile an edit that cannot prove it kept them.

Quick facts

Version	Bend 2
Released	17 September 2026
License	Apache-2.0
GitHub stars	20,183
Compile targets	C, Metal, CUDA, JavaScript
Syntax	Python-like, with dependent types
Platforms	macOS and Linux (no Windows)

What is it?

A file called LAWS.bend is the new idea in Bend 2, which became publicly available on 17 September 2026. In it you state properties the program must always satisfy — a balance is conserved, two objects never overlap, a sort really sorts — and the compiler treats them as theorems it has to re-prove after every change. The language itself is Apache-2.0, has Python-like syntax with dependent types, and compiles to C, Metal, CUDA and JavaScript.

How does it work?

The type checker doubles as a proof checker. When code changes, Bend demands a mechanical proof that every declared law still holds, and it will not produce a binary otherwise; the documented workflow is to run `bend PROOF.bend` before committing. Parallelism comes from divide-and-conquer structure rather than explicit threads, so the same program spreads across cores or a GPU without thread code.

Why does it matter?

The usual complaint about AI-written code is that it looks right and quietly breaks an invariant somewhere else. Laws turn that review problem into a compile error, which is a different kind of guarantee than a linter or a test suite. The catch is stated in Bend's own repository: the compiler is 99% AI-written and not yet fully audited, and the language has no type inference, no macros and no Windows build.

Who is it for?

developers who want AI edits gated by proofs

Frequently asked questions

Is Bend 2 free to use?: Bend 2 is Apache-2.0 licensed and developed in the open at github.com/bendlang/bend, so it is free for commercial and personal work. Installation is a single shell command from bend-lang.com, and the repository ships the compiler, the guide and the proof checker together rather than splitting a paid tier out of the toolchain.
Do Bend 1 programs still run on Bend 2?: No. The Bend project states that Bend 1 programs do not carry forward to Bend 2, so existing code has to be rewritten rather than migrated. Bend 1 was a massively parallel functional language; Bend 2 keeps the parallel execution story but rebuilds the language around dependent types and checked program laws, which is why compatibility was dropped.
What can Bend 2 not do yet?: The Bend 2 repository lists its own limits plainly: no type inference, no macros, no separate compilation, no multi-machine execution, no Windows support, and only three numeric types — Nat, U32 and F32. Native compilation is also described as slow. These are documented gaps rather than bugs, so early users should expect to write more type annotations than usual.
How much of the Bend 2 compiler was written by AI?: The Bend repository says the compiler is 99% AI-written and has not been fully audited yet. That is an unusual disclosure for a tool whose selling point is mechanical trust, and it is the main caveat for anyone considering Bend 2 for safety-relevant code: the proof checker's own implementation has not had the human review that its output is meant to replace.
How fast is Bend 2 at checking proofs?: Bend's project page claims its proof checker beats other proof assistants by several orders of magnitude, verifying proofs in under a second where competing tools take minutes. Those are the project's own published figures rather than independent measurements, and the repository also claims C-level speed on CPUs and CUDA-level throughput on GPUs for ordinary programs.

Try it

curl -fsSL https://bend-lang.com/install.sh | sh