It is possible to apply for a settlement permit C after possessing a B permit for 5 or 10 years in Switzerland depending on the nationality of the applicant. Applications can be made no more than 3 months before the expiry of the current permit.
The nationals of most EU countries, the US, Canada, and now the UK receive the settlement permit C after five years if they can prove the required level of language proficiency (see below) and fulfill the integration criteria set out in 2019, including no criminal record or dependence on social welfare.
Third-country nationals can apply for this permit ordinarily after 10 years or apply for the fast-track C permit after 5 years if they can prove a higher language and integration level.
Until recently, there were a number of EU countries that had bilateral agreements with Switzerland, exempting their citizens from the requirement to provide evidence of language proficiency.
These exemptions have ended and from the 1st of February 2023, all C permit applicants must include certified proof of the local language at level A1/A2.
Further information (on language requirements and other criteria) can be found on the Fachstelle Migration Zug website, where you can also sign up for their Foreigners and integration law (AIG) event.