I think they're intentionally keeping midsize under their wraps until investor day. I did notice this image in the investor documents:
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To me, it looks like they're well-passed midsize's design stage if they're already hinting at robotaxi hardware integration.
The most recent investor call mentioned that they have completed the first production validation models for midsize. Winterhoff also claimed that total costs of midsize components were below costs estimates and that the Saudi Arabia facility is slightly ahead of schedule on construction. Since midsize is still on-track for end-of-year start of production, I believe these further add to my gut feeling that Lucid is intentionally keeping their cards close to their chest for midsize's reveal.
Personally, I think that they're doing this so that when they do have the official midsize reveal, they can strike while the iron is hot and emphasize the EOY start of production. I can only hope that the knockdown Air and Gravity kits being sent to the Saudi Arabia plant have given the teams the hands-on experience they need for scaling up midsize. Winterhoff has also stressed about waiting for the investor day for more midsize news, so I think we should wait until then.