This is related to maintenance on the NERSC Spin service. See this page for more details: MOTD
When the Spin service is restored to normal operations, the legacy Materials Project website and API should also come back online.
We apologise for any inconvenience this might cause in the interim, and recommend users use the new Materials Project website at materialsproject.org or, equivalently, at next-gen.materialsproject.org.
Regards,
Matt
Still ongoing. Just a note that this downtime causes spurious pymatgen CI failures: Fix `TqdmExperimentalWarning`: Using `tqdm.autonotebook.tqdm` in notebook mode · materialsproject/pymatgen@959fbc4 · GitHub
pymatgen.ext.matproj.MPRestError: REST query returned with error status code 403. Content: b’{“valid_response”: false, “error”: “API_KEY is not a valid key.”, “version”: {“db”: “2020_09_08”, “pymatgen”: “2022.0.8”, “rest”: “2.0”}, “created_at”: “2022-10-10T10:40:21.838098”}’
thank you
As the spin service is restored to normal, may I ask when will the legacy MP and API come back online? Many thanks! 
Does this mean that there is a legacy API as compared to some newer API? I’ve been working with pymatgen.ext.matproj.MPRester (I can’t figure out how to check the version number)
The Spin service has not yet been restored to normal, as shown on the MOTD page under “Service Status,” and we are still waiting to hear more. When it has been restored, we hope to have the legacy website back online very quickly at some point during the next working day (9am-5pm US/Pacific).
Does this mean that there is a legacy API as compared to some newer API? I’ve been working with pymatgen.ext.matproj.MPRester (I can’t figure out how to check the version number)
Please consult the table at Materials Project - API, or the documentation available at Differences between new and legacy API - Materials Project Documentation
Best,
Matt
We have been advised by NERSC that a full-day maintenance will occur later this week or early next week to resolve the issue.
Our cloud-based infrastructure remains unaffected, and users are recommended to use the new/next-generation Materials Project website and API at materialsproject.org, which also has the latest and most up-to-date data available.
This outage has now resolved thanks to the hard work of the Spin team at NERSC.
Thank you very much!