As noted elsewhere (prompt-toolkit/python-prompt-toolkit#432), prompt_toolkit lacks a mechanism for the history search prompt to be customized for vi mode. The default inside prompt_toolkit is emacs mode, so vi mode users are shown the emacs mode history search prompt (e.g. "I-search: ", "I-search backward:") instead of "/" or "?". When the prompt_toolkit issue is resolved, please update IPython to pass the appropriate argument (likely editing_mode) to create_prompt_layout.