The make-vocab subcommand allows you to create a vocabulary from your dataset[s], which you can then reuse without recomputing it each training run.

$ allennlp make-vocab --help

 usage: allennlp make-vocab [-h] [-o OVERRIDES] [--include-package INCLUDE_PACKAGE] param_path

 Create a vocabulary from the specified dataset.

 positional arguments:
 param_path            path to parameter file describing the model and its

 optional arguments:
 -h, --help            show this help message and exit
 -o OVERRIDES, --overrides OVERRIDES
                       a HOCON structure used to override the experiment
 --include-package INCLUDE_PACKAGE
                         additional packages to include