# Release notes for MUSE v1.6.0 (May 8, 2026)

These are the main changes in MUSE v1.6.0.

## New `merit-order` dispatch method ({github}`838`)

- New dispatch method which dispatches assets in each timeslice starting with the cheapest first (lowest marginal cost) until demand is fully met.
- This method is best suited to sectors where supply is pooled across assets and short-run marginal cost is the dominant driver of dispatch decisions (e.g. electricity production).
- This can be enabled by specifying `dispatch_production = "merit-order"` in the settings toml file for the relevant sector(s). See documentation [here](https://muse-os.readthedocs.io/en/latest/inputs/toml.html#standard-sectors).
- Several of the example and tutorial models have been updated to use this new method.

## Change the way capacity constraints are applied ({github}`831`)

- Fixes an issue affecting capacity constraints in models with multiple
agents. Whereas previously entire capacity allowances were applied to each agent, allowances for each agent are now scaled according to the agent's quantity.
- For example, if a technology has an addition limit of 100 MW per year, then an agent with a quantity of 0.5 would have an addition limit of 50 MW per year (noting that quantities for all agents should sum to 1).
- See updated documentation [here](https://muse-os.readthedocs.io/en/latest/inputs/technodata.html) for more details.

## Adds support for Python 3.14, and drops support for Python 3.9 and 3.10 ({github}`826`)

- Since several MUSE dependencies have dropped support for Python 3.9 and 3.10, MUSE v1.6.0 drops support for these versions of Python. This also allows us to add support for Python 3.14.
- If you were previously using Python 3.9 or 3.10, you must create a new environment using 3.11 or later. There are instructions on setting up a new environment with the appropriate Python version [here](https://muse-os.readthedocs.io/en/latest/installation/virtual-env-based.html).

## Small fixes

- Remove un-produced commodities from the sector "costs" output file ({github}`834`).
- MUSE previously returned input prices (or zero for commodities with no input prices defined) in the global "prices" output file for the simulation’s base year, rather than endogenously calculated prices. This has now been corrected so that endogenously calculated prices are returned from the base year onward. See {github}`835`.
- Improved documentation for the [projections file](https://muse-os.readthedocs.io/en/latest/inputs/projections.html).