What Is the SO-101 Robot Arm? A Buying and Naming Guide
Everything you need to make sense of the SO-101: what it is, how the SO-100, SO-101 and SO-ARM names relate, why an assembled arm beats a kit for most people, and where to get one ready to run with LeRobot.
The SO-101 is an open-source desktop robot arm with 5 degrees of freedom plus a parallel gripper, built on Feetech STS3215 smart servos and a 3D-printed body, and fully compatible with Hugging Face LeRobot. It is the current version of the SO-ARM100/SO-101 design. Hashtag Robotics sells it assembled and tested, so you skip the build and start working right away.
What is the SO-101
The SO-101 is a compact, open-source robot arm designed to sit on a desk and learn real tasks. It has 5 degrees of freedom plus a parallel gripper, which is enough to reach, rotate, and pick up everyday objects in a tabletop workspace.
Three things define it:
- Feetech STS3215 serial-bus smart servos. These chainable smart servos report position and load over a single bus, so the arm is both the actuator and the sensor for learning.
- A 3D-printed body (PLA or PETG), based on the open SO-ARM100/SO-101 design. The mechanical files are public, which is what makes the platform open source.
- Hugging Face LeRobot compatibility. From Python you can teleoperate the arm, collect demonstration data, train imitation-learning policies, and run those policies back on the hardware.
In short, the SO-101 is one of the most accessible ways to get into hands-on robot learning without building a full industrial cell.
The naming maze: SO-100, SO-101, SO-ARM100, SO-ARM101
The naming around this arm trips up a lot of first-time buyers. The good news is that it is simpler than it looks. SO-100 is the earlier version and SO-101 is the current one, and the SO-ARM names are just the longer form of the same family.
| Name | What it refers to | What differs | LeRobot family |
|---|---|---|---|
| SO-100 | The earlier generation of the open arm design. | The first widely adopted revision. Refinements later landed in the SO-101. | Yes |
| SO-101 | The current generation, and the one to choose for new builds. | The up-to-date revision of the same arm. This is what Hashtag Robotics ships. | Yes |
| SO-ARM100 | The same arm as SO-100, written in the longer family naming. | A naming alias, not a different robot. Maps to the SO-100 generation. | Yes |
| SO-ARM101 | The same arm as SO-101, written in the longer family naming. | A naming alias, not a different robot. Maps to the SO-101 generation. | Yes |
So if you see SO-100, SO-101, SO-ARM100 or SO-ARM101, you are looking at the same arm family. The number, 100 or 101, tells you the generation. For a new setup today, SO-101 (SO-ARM101) is the version to pick.
Assembled vs DIY kit
Because the design is open source, you can source parts and build an SO-101 yourself, or you can buy one already built. The path you choose mostly comes down to how you want to spend your time.
| Assembled (Hashtag Robotics) | DIY kit / self-build | |
|---|---|---|
| Assembly time | None. It arrives built. | Printing, wiring, servo ID setup and calibration before first use. |
| Tested | Yes. Each arm is assembled and tested before it ships. | You test and debug it yourself. |
| Support | Backed by Hashtag Robotics as the seller. | Community docs and your own troubleshooting. |
| Who it suits | Researchers, educators, founders and developers who want to run LeRobot, not build hardware. | Makers who enjoy the build and want full control of every part. |
Both end up at the same open platform. The difference is where you start. If your goal is to collect data and train policies, an assembled and tested arm removes the hardware learning curve and gets you to the interesting part faster.
Leader vs follower
The SO-101 is usually used in a leader and follower configuration, which is how you teach it to do things.
- Leader arm. The operator-guided controller. You move it by hand, and its joint positions become the command signal.
- Follower arm. The task arm. It mirrors the leader and actually performs the work, like picking and placing objects.
To teleoperate, you guide the leader and the follower copies the motion in real time. To build a dataset, you record those demonstrations on the follower, then use them with LeRobot to train an imitation-learning policy. Once a policy is good enough, the follower can run on its own, without the leader.
What you can build with LeRobot
The reason the SO-101 matters is the software it plugs into. Hugging Face LeRobot is a Python toolkit for real-world robot learning, and the SO-101 is one of its supported arms. With it you can:
- Teleoperate the follower with the leader arm and feel the workflow end to end.
- Collect demonstration data by recording episodes of a task you perform by hand.
- Train imitation-learning policies on that data, so the arm learns from your examples.
- Run policy training and evaluation, then deploy the trained policy back onto the hardware to see it act autonomously.
That full loop, from teleoperation to data to a trained policy running on the arm, is exactly what makes the SO-101 a practical entry point into modern robot learning.
Where to buy the SO-101 assembled
Hashtag Robotics, the robotics arm of Hashtag World Company, sells the SO-101 in Turkey. We ship it assembled and tested, based on the open SO-ARM100/SO-101 design, including the leader and follower arms, so you can connect it and go straight to LeRobot.
Right now we are taking free pre-orders, with no payment collected yet. Reserving is a way to tell us you want one and to be first in line as we open availability.
Want to see it move first? Explore the interactive 3D model, then place a free pre-order on the SO-101 pre-order page.
Frequently asked questions
Is the SO-101 the same robot as the SO-ARM101?
Yes. SO-ARM101 is the longer family name for the SO-101 generation of the arm. Same hardware design, same Feetech STS3215 servos, same LeRobot compatibility.
Should I get the SO-100 or the SO-101?
For a new build, choose the SO-101. The SO-100 is the earlier version of the same design, while the SO-101 is the current one. Hashtag Robotics ships the SO-101.
Do I need to assemble anything?
No. Hashtag Robotics ships the SO-101 assembled and tested. There is no kit build, no servo ID setup and no print-and-wire step on your side.
What do leader and follower mean?
The leader is the arm you move by hand to control the system. The follower is the arm that mirrors the leader and performs the task. You teleoperate with the leader and record data on the follower.
Is it really compatible with Hugging Face LeRobot?
Yes. The SO-101 works with LeRobot in Python for teleoperation, data collection, imitation learning and policy training, then running those policies back on the arm.
How much does it cost and how do I order?
Hashtag Robotics is currently taking free pre-orders with no payment collected yet. Reserve yours on the pre-order page and we will follow up as availability opens.
SO-100, SO-101, SO-ARM100 and SO-ARM101 refer to the same open arm family. Hashtag Robotics ships the SO-101, assembled and tested.