Is Arm Open Source? Understanding Arm's Architecture, Licensing, and the Open Source Ecosystem

If you've been reading about chips, processors, or the shift away from x86 architecture, you've probably run into the term "Arm" more than once. And if you're wondering whether Arm is open source — the honest answer is: it depends on what part of Arm you're talking about. The architecture itself is proprietary. But around it, a rich open source ecosystem exists. Let's unpack what that actually means.

What Is Arm, Exactly?

Arm (originally Advanced RISC Machines) is a processor architecture — a set of instructions that defines how a CPU communicates with software. Arm Holdings, the company behind it, doesn't manufacture chips. Instead, it designs the architecture and licenses it to chipmakers like Apple, Qualcomm, Samsung, MediaTek, and NVIDIA, who then build their own processors based on those designs.

This is fundamentally different from how open source software works. Arm's Instruction Set Architecture (ISA) is a commercial product protected by intellectual property law.

The Core Answer: Arm's Architecture Is Proprietary

The Arm ISA is not open source. To design a chip that uses Arm instructions, a company must:

• Sign a licensing agreement with Arm Holdings
• Pay royalty fees per chip shipped
• Agree to usage terms that restrict what can and can't be modified

This is why you can't just download the Arm ISA, tweak it, and start manufacturing chips without legal consequences. Arm's business model is built entirely on this licensing structure — it's one of the most valuable IP portfolios in the semiconductor industry.

So Where Does Open Source Come In? 🔍

Here's where things get genuinely interesting. While the architecture itself is proprietary, several major components around Arm are fully open source:

Open Source Firmware and Software

• Linux kernel: Has supported Arm processors for decades. The Linux source code is open, even when it runs on Arm chips.
• GNU toolchain (GCC, Binutils): Open source compilers that generate Arm-compatible code.
• LLVM/Clang: Another open source compiler suite with strong Arm support.
• U-Boot: An open source bootloader widely used on Arm-based embedded systems.

Open Source Arm-Based Projects

• RISC-V (technically a separate architecture, not Arm) is often mentioned here because it is fully open source — and it's frequently compared to Arm for this reason.
• SystemReady and Arm's TF-A (Trusted Firmware-A): Arm has open-sourced its reference firmware under the BSD license.
• Arm Cortex-M reference implementations: Arm has made some reference software and development tools available through open repositories on GitHub.

Arm's Flexible Access and Developer Programs

Arm has expanded access through programs like Arm Flexible Access, which gives startups and developers limited access to IP for prototyping — but this is still a licensing program, not open source.

What About RISC-V — Is That the "Open Source Arm"?

This distinction matters a lot in discussions about open processor architectures. RISC-V is a genuinely open source ISA — free to use, implement, and modify without licensing fees. It's governed by RISC-V International, a nonprofit.

Many developers and researchers who want an open source alternative to Arm look to RISC-V for exactly that reason. The two are different architectures, but they often get compared because they're both RISC-based (Reduced Instruction Set Computing) designs.

Why the Confusion Exists

Several factors make this question genuinely murky:

Open source software runs on Arm. When people use a Raspberry Pi (Arm-based) running Linux with open source apps, the entire experience feels open. The hardware architecture underneath is proprietary, but everything visible to the user may be fully open source.

Arm has open-sourced specific components. Arm Holdings has selectively released firmware, tools, and reference designs on GitHub. This creates a partial picture that can look like full open source if you're not looking closely.

"Open" is used loosely. Terms like "open platform," "open ecosystem," and "open architecture" don't necessarily mean open source in the GNU/FSF sense. Arm uses some of this language in marketing without implying the ISA itself is freely licensed.

Factors That Affect How "Open" Your Arm Experience Is 🛠️

Whether Arm's proprietary nature actually affects you depends on your context:

• Embedded developers working with Arm Cortex-M microcontrollers will interact heavily with open source toolchains but still operate within Arm's licensing boundaries at the silicon level.
• Consumer device users (Android phones, MacBooks with Apple Silicon) are rarely affected — the licensing happens between Arm and the chipmaker.
• Researchers and open-hardware advocates may find Arm's closed ISA a meaningful limitation compared to RISC-V.
• Enterprise software teams running workloads on Arm cloud instances (AWS Graviton, Ampere) are mostly concerned with software compatibility, not licensing.
• Chip designers and startups feel Arm's licensing structure most directly — costs and restrictions vary significantly by tier and use case.

The Gap That Remains

Understanding Arm's open source status at the architectural level is one thing. Whether that matters to you — practically speaking — hinges on what you're actually trying to do. A hobbyist running Linux on a Raspberry Pi has a very different relationship with Arm's licensing than a hardware startup designing a custom SoC, or an enterprise architect choosing between x86 and Arm cloud instances for a production workload.

The architecture is proprietary. The ecosystem built on top of it is substantially open. Where those two realities intersect for your specific project, device, or use case is the piece only you can work out.