Nextflow versions
Current supported Nextflow syntax version & requirements¶
As of version 3.0 of the training portal, all our training courses are based on the 25.10.2 version release of Nextflow unless otherwise specified on the course index page (except deprecated or otherwise archived materials which may not include a version notice).
Because the courses now use typed inputs at the workflow level as well as workflow-level output directives, they require the use of the V2 syntax parser. If you plan to use the environment we provide through Github Codespaces or local devcontainers, you don't need to do anything unless specifically noted in the course instructions. However, if you are planning to work through the trainings in your own environment (Manual install), you will need to make sure to use Nextflow version 25.10.2 or later with the v2 syntax parser enabled.
Older versions of the training materials¶
Our training materials have been versioned since February 2025.
You can access older version of the training materials that work with versions of Nextflow before 25.10.2 via the dropdown menu item at the top of every page that shows the numbered version of the training materials. When you select an older version of the training materials, links to the training environment will automatically specify the corresponding version of the environment.
Other information about Nextflow syntax versions¶
Nextflow has two distinct versioning concepts that are sometimes confused: DSL versions and syntax parser versions.
DSL1 vs DSL2 refers to fundamentally different ways of writing Nextflow pipelines.
DSL1 was the original syntax where processes were implicitly connected through channels.
DSL2, introduced in Nextflow 20.07, added modularity features: the ability to import processes and workflows from other files, explicit workflow blocks, and named process outputs.
DSL1 was deprecated in Nextflow 22.03 and removed in 22.12.
All modern Nextflow code uses DSL2.
Syntax parser v1 vs v2 refers to different parsers that both work with DSL2 code. The v1 parser is the original, more permissive parser. The v2 parser is stricter and enables new language features such as static typing (typed inputs and outputs) and workflow-level output directives. The v2 parser also provides better error messages and catches more errors at parse time rather than at runtime. The v2 parser will become the default in Nextflow 26.04.
In summary: DSL2 is the language you write; the syntax parser version determines how strictly that language is interpreted and what advanced features are available.
Checking and setting the Nextflow version¶
You can check what version of Nextflow is installed on your system using the command nextflow --version.
For more information about how to update your version of Nextflow, please see the reference documentation on Updating Nextflow.
Enabling the v2 syntax parser¶
To enable the v2 syntax parser for your current session, run the following command in your terminal:
To make this permanent (pending v2 becoming the default in Nextflow 26.04), add the export command to your shell profile (~/.bashrc, ~/.zshrc, etc.):
Note that the NXF_SYNTAX_PARSER=v2 environment variable is a temporary requirement.
From Nextflow 26.04 onward, the v2 parser will become the default and this setting will no longer be needed.
Disabling the v2 syntax parser¶
To disable the v2 syntax parser for your current session, run the following command in your terminal:
Migrating existing code¶
For guidance regarding the migration of existing code to comply with more recent versions of Nextflow, please see the Migration Notes in the reference documentation.
These two articles are particularly helpful for migrating to the most recent release:
Both of these features are covered as part of the beginner training starting in version 3.0 of the training materials.
Depending on the generation of Nextflow code you intend to migrate, you may be able to get most of it done by the Nextflow linter using the nextflow lint -format command.
See the CLI reference for lint for more details.
We hope this will be helpful. If you need help, reach out on Slack or on the forum.
