Gen1 vs Gen2 Resource Classes: Summary

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, and Remote Docker.

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

At a glance

Docker executor (x86)

Resource classes

Availability

What Gen2 Docker does not include

Linux VM executor (machine, x86)

Resource classes

Availability

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. 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

Gen2 mapping (x86)

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 does not currently support IP Ranges.
• Gen2 resource classes are not currently available for Arm-based Remote Docker.

Arm Remote Docker

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

Feature support matrix

Performance and credits

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.

Additional resources

• Using Docker: Docker gen2
• Run Docker commands: Specifications and mapping
• Configuration Reference: resource classes
• Linux VM Gen2 support policy
• IP Ranges
• Introducing Gen2 Docker (x86)
• Gen2 Linux VM / (x86) Remote Docker GA
• Docker 28 and 29 on Remote Docker Gen2
• CircleCI price list