Phi-1.5

Phi-1.5 is a 1.3-billion-parameter Transformer from Microsoft Research, released in November 2023 as the follow-up to Phi-1. It was trained on the same synthetic textbook-quality sources as Phi-1 plus new NLP synthetic texts, giving it common-sense reasoning and language understanding comparable to models five times larger.

It was released as a base model without instruction tuning or RLHF, under the MIT license, as a research playground for studying safety, toxicity, and fine-tuning in small models. It kicked off the Phi small-language-model line that continued through Phi-2, Phi-3, and Phi-4.