The distinction between using “a” vs “an” is one based on the immediately proceeding syllable sound rather than the letter. If it’s proceeded by a vowel, then use “an”, and if it’s proceeded by a consonant, use “a”.
Because “LLM” is pronounced “el el em”, the first syllable sound is “eh”—a vowel.
The same letter may need different “a”/“an” article based on how the word is pronounced. For example “an LLM” vs “a layer”.
The distinction between using “a” vs “an” is one based on the immediately proceeding syllable sound rather than the letter. If it’s proceeded by a vowel, then use “an”, and if it’s proceeded by a consonant, use “a”.
Because “LLM” is pronounced “el el em”, the first syllable sound is “eh”—a vowel.
The same letter may need different “a”/“an” article based on how the word is pronounced. For example “an LLM” vs “a layer”.
See this for someone smarter than me explain it: https://www.merriam-webster.com/grammar/is-it-a-or-an