As of October 2023, the end of the light novel series "That Time I Got Reincarnated as a Slime" (Tensei shitara Slime Datta Ken) features Rimuru Tempest at an incredibly high power level. By the later volumes, Rimuru has achieved numerous powerful forms and abilities. He has the capacity to contend with divine beings and other high-tier entities, showcasing incredible skills such as reality manipulation, time manipulation, and various forms of magic.
Rimuru's character development leads him to not only become immensely powerful but also to ascend to the role of a ruler with a deep understanding of governance, justice, and compassion. His powers include his evolution into a True Dragon and eventually becoming the Supreme Being known as "Rimuru," which places him on a level where he can face off against some of the most formidable characters in the universe.
In terms of scaling, Rimuru's power, particularly in the later volumes, can be viewed as exceptionally high within the context of the series, often placing him among the strongest characters across the various realms, including gods and other legendary figures. Comparisons to other characters from different series can be difficult due to the unique rules of the respective universes, but within his own universe, Rimuru is portrayed as one of the apex beings.
For a comprehensive view on the scale, it's advisable to read the latest volumes of the light novel and any associated materials that detail the extensive mechanics of power and abilities in the series.