Gen1 and Gen2 are both CircleCI resource class families, but they are not drop-in replacements for each other. Some sizes, platforms, and features differ by executor.

This article puts the main Gen1 vs Gen2 differences in one place for Docker, Linux VM, Remote Docker, and Arm.

For full CPU, RAM, and credit rates, see the price list and the configuration reference.

At a glance

Topic	Gen1	Gen2
Naming	Classic names (`small`, `medium`, `large`, …)	Names end in `.gen2`. Available sizes depend on the executor
Docker sizes (x86)	`small` through `2xlarge+`	`small.gen2` through `2xlarge+.gen2`
Remote Docker sizes (x86)	Documented mapping, including `small` → `medium` and `medium+` → `large`	Starts at `medium.gen2`. `small.gen2` is not supported for Remote Docker
Credits / minute	See price list	Gen2 Docker costs more credits per minute than Gen1. See price list for Linux VM Gen2 rates. Arm Gen2 preview pricing may change at general availability
CircleCI Cloud	Supported	Supported
CircleCI Server	Supported for documented Gen1 Docker and Linux VM classes	Not supported for Gen2 Docker (x86 and Arm) or Gen2 Linux VM (x86 and Arm)
IP Ranges	See IP Ranges for executor support	Supported on x86 Docker Gen2 IP ranges support available for Gen2 Docker (x86)
Arm Docker	Supported	Supported (beta, Cloud only)
Arm Linux VM (`machine`)	Supported	Supported (beta, Cloud only)
Arm Remote Docker	Supported	Not yet available
Free plan + Docker	Resource class access depends on your plan	Gen2 Docker requires a paid plan
Gen2 Linux VM / x86 Remote Docker availability	Gen1 Linux VM and Gen1 Remote Docker are already available (separate from Gen2)	Available for all users

Docker executor (x86)

Resource classes

Size	Gen1	Gen2
small	`small`	`small.gen2`
medium	`medium`	`medium.gen2`
medium+	`medium+`	`medium+.gen2`
large	`large`	`large.gen2`
xlarge	`xlarge`	`xlarge.gen2`
2xlarge	`2xlarge`	`2xlarge.gen2`
2xlarge+	`2xlarge+`	`2xlarge+.gen2`

Availability

Spec	Gen1	Gen2
Cloud	Yes	Yes
Server	Yes	No
Plan	Resource class access depends on your plan	Paid plans only

What Gen2 Docker (x86) does not include

Item	Gen2
Free plans	Not supported
Remote Docker with `small.gen2`	Not supported. Smallest Remote Docker size is `medium.gen2`
CircleCI Server	Not supported

Linux VM executor (machine, x86)

Resource classes

Size	Gen1	Gen2
medium	`medium` (2 vCPU / 7.5 GB)	`medium.gen2` (2 vCPU / 8 GiB)
large	`large` (4 vCPU / 15 GB)	`large.gen2` (4 vCPU / 16 GiB)
xlarge	`xlarge` (8 vCPU / 32 GB)	`xlarge.gen2` (8 vCPU / 32 GiB)
2xlarge	`2xlarge` (16 vCPU / 64 GB)	`2xlarge.gen2` (16 vCPU / 64 GiB)
2xlarge+	`2xlarge+` (32 vCPU / 64 GB)	`2xlarge+.gen2` (32 vCPU / 128 GiB)

Availability

Spec	Gen1	Gen2
Cloud	Yes	Yes
Server	Yes	No
Disk	150GB	150GB

Both Linux VM tables start at medium / medium.gen2. small.gen2 is a Docker class, not a Linux VM class.

Gen2 Linux VM images

Gen2 machine resource classes on CircleCI Cloud support these Ubuntu LTS versions:

Ubuntu 22.04
Ubuntu 24.04
Ubuntu 26.04

Supported tags include current and edge. Dated tags are not supported for Gen2 resource classes. Gen2 resource classes are not available on CircleCI Server.

Remote Docker (setup_remote_docker)

Remote Docker uses a Linux or Arm machine resource class based on the Docker executor resource class you set. Gen1 and Gen2 use different size lists.

Gen1 mapping (x86)

A Remote Docker environment uses a Linux VM that corresponds to the Docker executor class, with these exceptions:

small maps to medium
medium+ maps to large

Docker resource class	Remote Docker (Linux VM)
`small`	`medium`
`medium`	`medium`
`medium+`	`large`
`large`	`large`
`xlarge`	`xlarge`
`2xlarge`	`2xlarge`

Gen2 mapping (x86)

Docker resource class	Remote Docker (Linux VM)
`medium.gen2`	`medium.gen2`
`large.gen2`	`large.gen2`
`xlarge.gen2`	`xlarge.gen2`
`2xlarge.gen2`	`2xlarge.gen2`
`2xlarge+.gen2`	`2xlarge+.gen2`

Important differences:

small.gen2 is available for plain Docker Gen2, but it is not supported for Remote Docker. The smallest Gen2 Remote Docker size is medium.gen2.
medium+.gen2 is available for plain Docker Gen2, but it is not listed in the Gen2 Remote Docker mapping table.
Gen2 resource classes are not yet available for Arm-based Remote Docker.

Arm Remote Docker

	Gen1	Gen2
Classes	`arm.medium`, `arm.large`, `arm.xlarge`, `arm.2xlarge`	Not yet available

Remote Docker version pins

Remote Docker version tags are listed in the Remote Docker docs, including aliases such as default, edge, and previous, plus version tags such as docker29, docker27, and docker26. For Gen2, the changelog also documents pinning with docker28 and docker29. Check those pages for the current tag list.

Example from the Gen2 changelog:

resource_class: medium.gen2
steps:
   - setup_remote_docker:
       version: docker28

Arm (Gen2 beta)

Arm Gen2 resource classes are in beta for the Docker and Linux VM (Arm VM, machine) executors, and are available to all users. Gen2 Arm is not yet available for Remote Docker. Preview pricing may change at general availability. Arm Gen2 Docker and Arm Gen2 Linux VM classes are available on CircleCI Cloud only, not on CircleCI Server. See the Gen2 Arm beta changelog for details.

Arm resource classes

Size	Gen1	Gen2 (beta)	vCPUs / RAM	Gen2 credits / min (preview)
medium	`arm.medium`	`arm.medium.gen2`	2 vCPU / 8 GB	6
large	`arm.large`	`arm.large.gen2`	4 vCPU / 16 GB	12
xlarge	`arm.xlarge`	`arm.xlarge.gen2`	8 vCPU / 32 GB	24
2xlarge	`arm.2xlarge`	`arm.2xlarge.gen2`	16 vCPU / 64 GB	48

The Arm VM (machine) classes have a 100 GB disk for both Gen1 and Gen2. Credit rates are the same for Arm Gen2 Docker and Arm Gen2 Linux VM. They are preview pricing and may change at general availability.

Availability

Executor	Gen1	Gen2 (beta)
Arm Docker	Cloud only	Cloud only
Arm Linux VM (`machine`)	Cloud and Server	Cloud only
Arm Remote Docker	Yes	Not yet available

Arm Gen2 images and examples

For the Arm Linux VM executor, Arm Gen2 resource classes are supported only on these images and tags:

ubuntu-2404:current and ubuntu-2404:edge
ubuntu-2604:current and ubuntu-2604:edge

Arm Linux VM example:

jobs:
  my-job:
    machine:
      image: ubuntu-2404:current
    resource_class: arm.large.gen2
    steps:
      - run: uname -a

Arm Docker example:

jobs:
  build:
    docker:
      - image: cimg/base:current
    resource_class: arm.large.gen2
    steps:
      - run: uname -a

For Arm Docker, use an image that publishes a linux/arm64 variant. You can check the OS/ARCH column on the image's tags tab on Docker Hub.

Feature support matrix

Feature	Gen1	Gen2
Plain Docker (x86)	Yes	Yes, paid plans
Remote Docker (x86)	Yes, with `small` → `medium` and `medium+` → `large` mapping	Yes, from `medium.gen2` through `2xlarge+.gen2`. `small.gen2` not supported. `medium+.gen2` not listed
Linux VM (`machine`, x86)	Yes	Yes, from `medium.gen2` through `2xlarge+.gen2`
IP Ranges	See IP Ranges	Supported on x86 Docker Gen2
Arm Docker	Yes	Yes, beta (Cloud only)
Arm Linux VM (`machine`)	Yes	Yes, beta (Cloud only). Requires `ubuntu-2404` or `ubuntu-2604` `current`/`edge`
Arm Remote Docker	Yes	Not yet available
CircleCI Server	Yes for documented Gen1 Docker and Linux VM classes	Not supported for Gen2 Docker (x86 and Arm) or Gen2 Linux VM (x86 and Arm)
Free plan Docker	Resource class access depends on your plan	Gen2 Docker not supported on Free. Paid plan required

Performance and credits

Product	Gen2 performance	Credits
Docker Gen2	Nearly 1.4x faster than Gen1	Higher credits/min than Gen1
Linux VM / (x86) Remote Docker Gen2	Up to 180% faster for multi-threaded workloads	See Gen2 rows on the price list
Arm Docker Gen2 (beta)	Up to 94% faster than Gen1, based on beta benchmarks	6 to 48 credits/min (see Arm resource classes above). Preview pricing, may change at general availability
Arm Linux VM Gen2 (beta)	Up to 73% faster than Gen1, based on beta benchmarks	6 to 48 credits/min (see Arm resource classes above). Preview pricing, may change at general availability

Same size names can mean different RAM across executors. Example: Docker medium.gen2 is 2 vCPU / 4GB. Linux VM medium.gen2 is 2 vCPU / 8 GiB. Actual Arm Gen2 gains depend on your workload and may change when Arm Gen2 becomes generally available.

Additional resources

How do I run commands in the remote Docker environment and understanding how this mirrors Docker in Docker?

Gen1 vs Gen2 Resource Classes: Summary

At a glance

Docker executor (x86)

Resource classes

Availability

What Gen2 Docker (x86) does not include

Linux VM executor (machine, x86)

Resource classes

Availability

Gen2 Linux VM images

Remote Docker (setup_remote_docker)

Gen1 mapping (x86)

Gen2 mapping (x86)

Arm Remote Docker

Remote Docker version pins

Arm (Gen2 beta)

Arm resource classes

Availability

Arm Gen2 images and examples

Feature support matrix

Performance and credits

Additional resources