LLM is the one everybody’s heard of. SLM (small language model) is the one that might be sitting on your phone right now, doing more of the work than you’d guess. Same basic technology, pretty different sizes, and the size decides where the thing can run and what it costs to use.
People treat “small” like it means “worse.” A lot of the time it just means cheaper and closer to you.
LLM
A large language model is the big kind, the models behind ChatGPT, Claude, and Gemini. They’re trained on enormous amounts of text and have hundreds of billions of Parameters (the adjustable numbers a model learns during training). They run in giant data centers. The companies mostly stopped publishing exact sizes, so a lot of the numbers you see online are educated guesses. When somebody says “AI” in a meeting, this is usually what they mean.
They know a lot, they reason fairly well across a huge range of topics, and they cost real money every single time someone uses them. That cost is why every company building on them watches the bill.
SLM
A small language model is the same idea at a size that fits on a laptop, a phone, or a cheap server. There’s no official cutoff, but “small” usually means somewhere under about 10 billion parameters. Apple’s on-device model is about 3 billion. Microsoft’s Phi-4-mini is 3.8 billion. Google’s Gemma 3 comes in sizes from 1 billion up to 27 billion (which is stretching the word “small” a bit, honestly).
They know less, and they’re weaker at hard, multi-step reasoning. But they’re fast, they can work without an internet connection, and your data can stay on your device. For a lot of everyday jobs (sorting email, pulling a date out of a document), small is plenty. Apple uses its small model for things like summarizing notifications right on the phone. NVIDIA researchers argued in June 2025 that running a 7-billion-parameter model is 10 to 30 times cheaper than running one with 70 to 175 billion.
The tell
Ask where it runs. If it needs a data center and a subscription, it’s an LLM. If it keeps working when your phone’s in airplane mode, it’s almost certainly an SLM.
Plenty of products use both, handing easy questions to a small model and hard ones to a big one. You usually won’t be told which one answered you.