Jurassic (models) is a family of proprietary large language models developed by the Israeli AI company AI21 Labs. The family comprises two generations, Jurassic-1 (2021) and Jurassic-2 (2023), both autoregressive decoder-only Transformer models served through the company's AI21 Studio API. The line was effectively retired when AI21 shifted to Jamba, a hybrid state-space-Transformer architecture, in 2024.
Jurassic-1
Jurassic-1, announced in August 2021, was among the first commercial models positioned as a direct alternative to OpenAI's GPT-3.1 Its largest variant, Jurassic-1 Jumbo, was developer-reported at 178 billion parameters, marginally larger than GPT-3's 175 billion and, at launch, one of the largest dense models publicly available for paid use alongside contemporaries such as Megatron-Turing NLG. AI21 chose a shallower and wider layer configuration than GPT-3, citing internal research on depth-to-width trade-offs, and used an unusually large tokenizer vocabulary of roughly 256,000 items that included multi-word expressions, which the company said improved token efficiency on English text.1 A smaller variant, Jurassic-1 Large (developer-reported at 7.5 billion parameters), was offered for lower-latency use. In 2022 AI21 also demonstrated Jurassic-X, a research system that routed queries from the language model to external calculators and search modules.
Jurassic-2
Jurassic-2, released in March 2023, replaced the first generation with three sizes (ultimately marketed as Light, Mid, and Ultra) whose parameter counts were not disclosed.2 The generation added non-English capability in several European languages, an 8,192-token context window, and variants adapted for following instructions, reflecting the industry turn toward instruction-tuned deployment after ChatGPT. Jurassic-2 models were also distributed through Amazon Bedrock, where they sat alongside first-party Amazon Titan models and other third-party offerings.3
Legacy
The Jurassic line marked AI21 Labs as one of the few startups fielding frontier-scale dense models in the early 2020s. In March 2024 the company introduced Jamba, moving away from pure Transformer designs, and subsequently deprecated the Jurassic-2 API models. Task-specific AI21 products such as Wordtune drew on the same underlying model family.