Only since 2023.

WDYM? It used an encoder-decoder transformer model long before 2023 (and also long before decoder-only transformers à la GPT became the new standard).

Most people seem to believe LLM only describe these decoder-only architectures, but the term predate them by a big margin. BERT (encoder-only) was a large language model, and there were even language models before transformers were even a thing.