LlamaIndex

pip install llama-index llama-index-llms-openai-like llama-index-embeddings-openai-like

import os
from llama_index.llms.openai_like import OpenAILike

llm = OpenAILike(
    model="openai/gpt-5-nano",
    api_key=os.environ["PHASEO_API_KEY"],
    api_base="https://api.phaseo.app/v1",
    is_chat_model=True,
)

response = llm.complete("Write one sentence about retrieval quality.")
print(response)

from llama_index.core import Settings

Settings.llm = llm