Okay, after looking a LOT up: Pimsleur said on their official subreddit, that Japanese levels 1-5 have 2500 unique words. I also confused myself a bit earlier today, mixing up Pimsleur with Glossika. Pimsleur lessons generally have LESS vocabulary than some alternatives. Glossika generally has more vocabulary taught than Pimsleur. I am actually using the glossika audio files currently, NOT pimsleur.
My usual conclusions on pimsleur stand though: based on what other pimsleur users said (that the whole course only covers the material Genki 1 has), and that it has around 20 words taught each lesson, with around 2500 words if you do ALL lessons, then its not the particular program i'd choose. Its good if youre a beginner, and intend to do all 5 levels. If you are not a beginner, it may only review words you know. If you're learning on your own, consider how much you study: if you want to learn 2500 words within a certain time frame (like a year) then make sure you complete pimsleur lessons frequently enough to finish the lessons in a year (or whatever your goal is). 2500 words, or Genki 1 and 2 book's 1700 total words (which pimsleur was compared to by a pimsleur user), are useful. But they arent intermediate, theyre words you'll want to learn as a beginner and then PROGRESS TO NEW MATERIAL. Do not dwell on pimsleur for 4 years, if your goal was to learn beginner words in 1-2 years and then move on to intermediate material (but if you are okay with it taking 4 years then of course go through lessons at the pace that works for your goals).
Some information on Glossika Japanese: the current 2024 course has around 6,400 sentences and teaches a bit over 5,000 words. I had this information given to me by an official glossika representative. Unfortunately, they did not know how much vocabulary was taught in the original audio-only Japanese glossika course, which was around half as big. Their current course seems to teach to N4 (maybe N3), as the representative felt a learner could go from the modern course glossika to simple anime like Shirokuma Cafe and learn words from immersion onward. The representative also stated glossika doesnt explicitly explain grammar, so if you are NOT a complete beginner then you'll have more success. Alternatively, if you are a complete beginner, reference a Grammar Guide (tae kims grammar guide, imabi.com, Genki textbooks etc) or use another source for beginner lessons like japanesepod101.com which has explanations. My rough guess would be that old glossika audio lessons taught between 2000-3000 words, because all old courses used the same base english sentences translated, and I remember for most languages that resulted in around 3000 unique words used. So old audio lessons Glossika will teach a bit more vocabulary than pimsleur, and significantly more than pimsleur by around 2000 additional words if you use the new glossika online courses. Increased vocabulary is a plus, but the end result will still be upper beginner/lower intermediate knowledge when you're done. I'd recommend glossika over pimsleur because more vocabulary is great in a language learning product.
These are what I actually recommend a learner start with. Because they're free. And they work.
Go on the Hoopla library app, or install Hoopla if you don't have the app yet. Register with one of your library memberships on Hoopla, it will give you access to tons of ebooks and audiobooks to check out. Now find: Japanese 1 Innovative Language. I personally found the audiobooks, Innovative Language has at least 9 levels of lessons from beginner to advanced. Unfortunately, I am having difficulty finding how much vocabulary all their lessons combined teaches. (A lot of language programs call some lessons Advanced when really you're only learning say the 1000-1500 most common words in them, which is still beginner level in terms of knowledge being studied or if you compare to textbook levels or language certification test levels). I am not sure if these lessons are the same as japanesepod101.com, but these lessons are similar, and they have a good amount of explanations so you can get grammar and cultural information as well as vocabulary - this means the course is more in depth than glossika or pimsleur, but it does teach a bit slower as there's more time that english is spoken. If you're a total beginner, or a beginner/lower intermediate learner who is looking for audio lessons with explanations, I recommend these. Theyre free! Theres a ton! Innovative Language also has a TON of lessons in multiple languages on Hoopla app, so browse.
Go to jaoaneseaudiolessons.com. Download the free 36 lessons, the free grammar guide, and the free transcripts. These lessons are FREE, they are made by people who have used stuff like Berlitz and Pimsleur and wanted to improve the method into something they'd find more useful. This site introduced me to the idea of "audio flashcards" audio of english then target language sentences. These lessons arent doing anything wild or new: what they are doing, is lessons like Glossika but with MORE explanation than glossika, and yet less english and less time wasting than stuff like Innovative Language. The biggest pro of this resource: they MADE a grammar guide you can use, they made a transcript so you can have your first reading material, and they made free audio. Ive used their audio lessons: they worked great for me. They worked better for me than Genki did (however Genki remains great for the speaking/writing skills i practiced with it), and helped pull me back into studying japanese. I am not sure how many words it teaches, a detail i wish ALL LANGUAGE LESSONS HAD TO MENTION. But my guess would be at least 1500 words. Their transcript book is 1075 pages, they usually introduce 1-7 new words per page, so on average 4 words, so the upper guess is they teach potentually 4,300 words in the 36 audio lessons. How is that for efficient? Even if these lessons only teach 1500 words (and i suspect the real words taught is probably the normal 2000-3000 of most beginner courses made well), at 36 lessons their lessons clock in as WAY less than Pimsleur or Glossika. These lessons recommend you listen to each lesson 5 times. So each lesson is 30-40 minutes (lets use 40 minutes per lesson), so 36 lessoms is 24 hours of listening material. Listen to each lesson 5 times, and you'll spend 120 hours on these lessons, not including time spent on the grammar guide or transcript. There is another reason i love japaneseaudiolessons.com: they wrote books that teach kanji with 1. Premade mnemonic stories (remember the heisig book expects you to make up your own stories which i found hard) 2. Mnemonic stories for meaning AND pronunciation (many premade mnemonic story resources like anki decks tend to only help with remembering definitions, not pronunciations), 3. Sentence examples to help you remember words, practice seeing them in context, and practice reading. Their books are by FAR my favorite kanji learning books. The kanji learning books do cost money, but i've found them useful and i was glad they existed. You do not need to buy the books, japaneseaudiolessons.com has a TON of free material that should get you through beginner level stuff. But if you, like me, like premade mnemonic stories including remembering pronunciations and example words in sentences, you may find checking out their kanji books is useful.