The Spitsbergen Treaty was signed in 1920 and it came into force in 1925. It sealed Norwegian sovereignty over the Svalbard archipelago (the name “Svalbard” was not used in the treaty) and regulates access for citizens of treaty member states.
Fredrik Wedel Jarlsberg, the Norwegian negotiator in Paris,
signed the Spitsbergen Treaty on 09th February 1920 in Versailles.
A range of countries have joined the treaty since 1925. Until recently, Latvia and North Korea (!) had been the latest new members. Both joined the treaty in 2016.
In April 2024, however, Ankara ratified their signature under the Spitsbergen Treaty. Since then, Turkey is the latest signatory country.
This will not change much in real life: Norway does not make a difference between citizens of member states and those from other countries. There are, for example, more than 200 people from Thailand and the Phillipines living in Longyearbyen. Their respective countries of origin are not members of the Spitsbergen treaty.
Turkey appears to be interested on a different level, as the Barents Observer writes: recently in July, a delegation from Turkey visited Pyramiden, a former Russian coal mining settlement in Isfjord, to look at the potential of running a research facility there. Russia has announced plans to develop Pyramiden as an alternative to Ny-Ålesund, where a range of countries run research facilities under Norwegian leadership.