Starting with 0.14.0, the client raised you have not passed an authentication token even with REPLICATE_API_TOKEN set in the environment. Maintainer mattt confirmed a behavior change in how the default client was initialized at import time caused the regression. The fix was merged in PR #170 and released in 0.15.4. Upgrading to 0.15.4 or later restores the old behavior of picking the token up from the environment.