Cas in 11.01 "I accept my transgressions and will accept any punishment you dole out" -- cool people understand Cas has always taken on accountability for things he's done. He screws things up but then accepts punishment. Sometimes to the point of self-blaming so hard we might worry about him.
Also his selflessness and love for Dean is showing.
Cas: Dean, I am fine. You tell me, the mark."
Dean: Oh really, you're worried about me after everything I--"
Cas: Dean, is it gone?
Dean: Yes, I'm good.
The visible relief Cas shows, the body language there--Cas leans his head back, eyes closed, his whole body goes into it. The weight of the MoC on Dean was so much it was like weight Cas carried with him--that is a strongly empathetic response. Cas's emotional IQ isn't that high, or his astuteness about feelings and how to people, but he does things like that on instinct because he cares very deeply and he is deeply connected to Dean.
But Cas also hides what he's going through and doesn't tell Dean-- because all that matters to him in that moment was Dean being okay--but Cas needs to learn to reach out when he needs help.
After Cas says goobye and it may be "some time before we see each other again" Dean starts freaking out calling Cas's name as Cas hangs up. Which is SO TYPICAL.
However there is character growth, because in 11.02, after being put through the wringer tortured by the angels, Cas finds his way to the bunker where Sam and Dean find him lying on the floor and he says "Help me." So Cas has learned to ask for help. He doesn't always stick to that growth, btw, but he does know and it's good to see when he does that.
Then in 11.03, which was directed by Jensen Ackles, mind you, Dean is quickest to Cas's side when he collapses in the bunker and he won't stop touching him. He also wraps a blanket around Cas and keeps petting him, and it looks like it's for Dean's comfort as much as for Cas's, it's okay Cas is still here he's going to be fine.
Dean's voice is so broken as he says Cas's name when he collapses after the attack dog spell is broken, he keeps saying Cas's name, Dean cradles his face and holds onto him.
Cas then wants to heal Dean from the impacts of the attack dog spell incidents and Dean refuses because "I had it coming." I still flinch at that. Dean still feels terrible about the MoC Dean library fight where he almost killed Cas and couldn't, even under MoC influence, he wouldn't kill Cas. It wasn't Dean's fault, he wouldn't have if he hadn't been charged up on killing under the MoC influence already, but Dean is still carrying that guilt around anyway, while Cas's only thought is that he wants to heal Dean. And doesn't blame him in the least.
Cas's face when Dean refuses the angel healing touch rips my heart out. We can see he wants to argue with Dean and tell him he's wrong and he should let Cas heal him. But Cas respects it and lets it go because that's what Dean wants.
11.04, Baby (which is a masterpiece episode and a great Sam and Dean ep but doesn't leave Cas behind) has Dean saying insistently over the phone, "Cas, you got one job to do and that's to heal." Despite Cas not being on screen in the ep, the ep was written to very much weave Cas as part of Sam and Dean's expanding family, and he is on the phone with Sam and Dean throughout the episode. Nobody wants to say Dean's term "werepire" until finally, Cas says it over the phone--but Dean can't hear it.
Then it's Cas shouting Dean's name insistently because he heard gunshots.
Dean also praises Cas for his research at the end, "good work, way to come off the bench."
Early season 11 with Dean and Cas, everyone.