June 27 (Reuters) - Artificial Intelligence chatbot

startup Character.AI said on Thursday it has launched a calls

feature that allows users to have voice conversations with their

AI characters, ratcheting up efforts to compete with rivals

including OpenAI.

AI-boom has prompted startups to release new features to

their chatbots as competitors such as Microsoft ( MSFT )-backed

OpenAI, Google and Amazon.com ( AMZN )-backed

Anthropic are looking to gain market share by engaging new

users.

The availability of free two-way voice calls on

Character.AI's app has come following OpenAI's announcement on

Tuesday that the ChatGPT maker's rollout of the advanced voice

mode of its latest model GPT-4o is delayed by one month.

Character.AI, co-founded by Noam Shazeer, who helped invent

"transformer" AI architecture while at Google that underpins

systems like Gemini and ChatGPT, enables users to create

customized AI companions with specific personalities and values.

The Menlo Park, California-based startup said the new calls

feature prompted more than 20 million calls from over 3 million

unique users in its early rollout, suggesting a strong

engagement.

Character.AI launched Character Voice, a suite of features

that allows users to hear characters speaking to them in

one-on-one chats, for all users in March.

Alphabet's Google was in talks to invest hundreds of

millions of dollars in Character.AI last year, two sources

briefed on the matter had told Reuters.