Levantine Arabic is not a dialect of Classical Arabic (Fus7a), according to the works of @Safaitic and @PhDniX.

Judge as of 2019-12-22. True: the published linguistic work of the people behind @Safaitic (Ahmad Al-Jallad) and @PhDniX (Marijn van Putten) holds that Levantine Arabic does not descend from Classical Arabic (it descends from other Old Arabic varieties), and this matches mainstream historical-linguistic opinion. Mostly true: their work supports the conclusion, but it is an inference from their findings rather than something they state directly, or the scholarly consensus mostly but not unanimously agrees. Mixed: their work supports the claim but the field is substantially divided. Mostly false: their work does not directly bear on this, or only partly supports it, or the conclusion is considered unproven. False: their work or the scholarly consensus holds that Levantine does descend from Classical Arabic.

Set before the research began.

1. E1 Wikipedia:Peer review/Levantine Arabic/archive2 - Wikipedia Wikipedia · 19 December 2021

   “Yet in the wake of epigraphic research beginning in the 19th century and the serious study of the modern vernaculars on their own terms, it is clear that Classical Arabic is a sister language to other forms of Arabic rather than their direct ancestor.”

2. E2 Talk:Arabic - Wikipedia Wikipedia · 24 August 2024

   “However, many varieties of Arabic both ancient and modern preserve features lost in Classical Arabic and present a state corresponding more closely to what is found in other Semitic languages (Al-Jallad 2018b, Huehnergard 2017, Pat-El 2017). This shows that these varieties of Arabic cannot have developed from Classical Arabic.”

3. E3 The Arabic Koine: Linguistic Evolution Language (Linguistic Society of America), hosted on Scribd · 1959

   “which was not identical with any of the earlier dialects and which differed in many significant respects from Classical Arabic but was used side by side with the Classical language during early centuries of the Muslim era.”

4. E4 Lebanese Arabic - Wikipedia Wikipedia

   “Historian and linguist Ahmad Al-Jallad has argued that modern dialects are not descendants of Classical Arabic, forms of Arabic existing before the formation of Classical Arabic being the historical foundation for the various dialects.”

E4 reports that Ahmad Al-Jallad (@Safaitic) has argued modern Arabic dialects do not descend from Classical Arabic but from earlier forms of Arabic. E1 quotes a statement that Classical Arabic is a sister language to other forms of Arabic rather than their direct ancestor. E2 quotes a passage, citing Al-Jallad, Huehnergard and Pat-El, which says such varieties cannot have developed from Classical Arabic. Ferguson's 1959 account (E3) describes a form of Arabic that differed in many respects from Classical Arabic and was used side by side with it. None of the evidence covers Marijn van Putten's (@PhDniX) work, and it reaches Al-Jallad's view mostly through Wikipedia pages and their talk pages. The evidence also does not show that the field agrees unanimously, so the claim fits "mostly true" rather than fully true.