Hello.
Currently having the same problem as others before with C4W3 assignment. Coursera grader only outputs “Your model could not be loaded. Make sure it is a valid keras file, if this is the case please let us know.” Tried different architectures/layer combinations with different sizes of the downloaded model. current version is ~11mb in size, around 1.1m trainable params. Model reaches mean loss of 300 after 38ish epochs. I’m a bit lost right now 
Thanks in advance
Send me your model function in a private message, let me have a look at it!
Hi. There is a compatibility issue with the Keras version that Colab recently updated to. It results in this error message when the grader tries to load your model:
Your model could not be loaded. Make sure it is a valid .keras file
The affected assignments are:
These notebooks have now been updated to rollback the Keras version. You can reopen them from the classroom. If you don’t want to rewrite your solution, you can simply add this to your old notebook (in the pip install cell before the imports):
!pip install keras==3.9.0
We’ll check if there are also effects on the other assignments this coming week.
Hope this helps!
@chris.favila, rollback to Keras 3.9.0 did the trick. Thank you very much! Thanks to @gent.spah as well for the quick response. The courses are awesome btw. Starting the next specialization right now.