Aya Expanse puts multilingual performance at the center
Cohere For AI’s release explores how to train for more than English-first usage.

Evaluate a multilingual model language by language, not only through one headline score.
Aya Expanse introduced eight-billion- and thirty-two-billion-parameter models aimed at multilingual tasks. The research account combines synthetic-data selection, preference training, safety tuning, and model merging, with evaluation material spanning twenty-three languages.
Its broader lesson is that multilingual quality is a training problem, not just a translation feature. The team describes sampling from different teacher models because a single teacher is unlikely to be equally capable across every language and domain.
Explore the release’s language-specific evaluations and model cards before choosing a checkpoint. For an application, build a small set of representative prompts in each target language. Aggregate benchmark wins alone do not tell you whether regional phrasing or specialist vocabulary works well.
Multilingual quality is not one number
A model described as multilingual may perform differently across languages, writing systems and domains. The useful question is whether it handles the languages and tasks a particular audience needs, including the forms of expression people actually use rather than only standardized evaluation sentences.
A customer-support application, for example, may receive mixed-language messages, local abbreviations and informal spelling. A benchmark result can help identify candidates, but it does not establish reliability on that combination of inputs.
Evaluate the task in each language
Use examples that reflect the same underlying task while preserving natural wording. Literal translations of an English test can introduce unnatural phrasing or miss culturally specific context. Where possible, involve fluent reviewers who understand the intended use.
Separate instruction following, factual accuracy and fluency. A response can sound natural while answering the wrong question, and a correct answer can be awkward enough to confuse the reader. Those outcomes need different fixes.
Include mixed and ambiguous inputs
People switch languages within a message and use names or technical terms that should not be translated. Test those cases directly. Also check whether the model follows a requested response language rather than drifting toward the language most prominent in its context.
For extraction tasks, verify that dates, amounts and named entities remain accurate. Surface fluency should not hide changes to the details that the downstream system uses.
Keep evaluation independent from localization
If prompts or examples are tuned with reviewer feedback, preserve a separate test set. Otherwise, repeated adjustment can make the system appear broadly improved when it has mainly adapted to the examples used during development.
Report results by language and task category rather than collapsing everything into one average. A deployment serving several communities should make an important weakness visible even if stronger performance elsewhere raises the overall score.
Review practical deployment conditions
Inspect the exact model’s terms, memory requirements and supported tooling. Measure the request lengths and concurrency the service expects. Different languages can produce different token counts for similar amounts of visible text, which can affect context limits and cost.
Provide an escalation or clarification path when the system is uncertain. A multilingual assistant should not pretend to understand a message it cannot reliably interpret.
The meaningful promise of multilingual model development is broader access to useful AI. That promise becomes real through language-specific evaluation, careful handling of local detail and an interface that treats every supported audience as a first-class user rather than assuming that strong English performance transfers automatically.
Source: A Deepdive into Aya Expanse: Advancing the Frontier of Multilinguality ↗ · johndang-cohere, shivalikasingh, dsouzadaniel, ArashAhmadian. How we write


