If the enemy's previous Magic action that was taken was the last one, the casting has been completed and the enemy is no longer casting. The enemy cannot abort casting the spell until their next turn unless they have a reaction that uses Concentration or prevents Concentration. On their turn, they can choose to take the next Magic action (continuing the spell or potentially completing it) or not to (aborting it).
As the primary caster, you take the Magic action to initiate casting a Circle spell. Until the Circle spell's casting is complete, you must maintain Concentration on the spell. If any caster's Concentration is broken, the spell fails.
The creator can end Concentration at any time (no action required).
Conclusion, a primary caster can abort the casting at any time.
Moving and Communicating take no actions but are still restricted to your turn. Ending Concentration requires no action to end on your turn. Nothing allows you to end Concentration as a non action outside of your turn. A spellcaster (any spellcaster in a Circle spell) can abort the casting at any time that they are eligible to end Concentration, which is only on their turn.
RAW, to see a creature casting a spell is to see the creature using components.
That's never stated in the 2024 rules or Sage Advice.
RAW changed from 2014 to 2024 and this might be an unintentional change or an intentional change, particularly if they had already considered the inclusion of Circle Magic and intended for the secondary casters to be valid targets if the spell casting was otherwise valid for targeting purposes.
Okay, I'm legitimately curious: How did you get it this wrong?
I didn't.
I have explained it multiple times already. If you do not understand the words I wrote that is one thing. If you do not agree with me and expect that by starting with the declaration that I am incorrect, I will magically buckle, I won't. Until we get a Sage Advice or Errata, I am correct. Until then, you are also correct. We both have valid readings. I will absolutely not back down from my reading being valid, but I will not declare yours invalid. I do not care intensely, what direction WotC chooses, only that they officially clarify their rules. Please, select another area of the conversation where I won't be repeating myself ad nauseum.
In essence, what they are establishing is that, yes, the act of being primary caster is essentially one of 'casting a spell' and we aren't suppose to try and argue 'well, they're taking the Magic action, but the spell requires the contribution of a group, so they aren't actually 'casting'.'
Absolutely not. It does not define initiation a Circle spell as casting a spell, if it did it would say so (which it doesn't do). But you are correct on the fact that we don't need to argue about if they are casting or not because the new trigger they defined for us will work anyway.
Initiating a Circle spell and contributing to one are both steps under Casting a Circle Spell. Cast a Circle spell follows rules for spellcasting in the PHB and also the rules for Circle spells. That said, I personally have less of an issue with saying that none of the spellcasters are casting a spell as opposed to only the primary caster is. In your view, I suppose the only opportunities for triggers when a spell is cast would be when the Circle spell is initiated (due the explicit call out) and when the spell completes (this would apply to an Arcane Trickster's Spell Thief and Order Domain's Voice of Authority)?
Moving and Communicating take no actions but are still restricted to your turn. Ending Concentration requires no action to end on your turn. Nothing allows you to end Concentration as a non action outside of your turn. A spellcaster (any spellcaster in a Circle spell) can abort the casting at any time that they are eligible to end Concentration, which is only on their turn.
I didn't.
I have explained it multiple times already. If you do not understand the words I wrote that is one thing. If you do not agree with me and expect that by starting with the declaration that I am incorrect, I will magically buckle, I won't. Until we get a Sage Advice or Errata, I am correct. Until then, you are also correct. We both have valid readings. I will absolutely not back down from my reading being valid, but I will not declare yours invalid. I do not care intensely, what direction WotC chooses, only that they officially clarify their rules. Please, select another area of the conversation where I won't be repeating myself ad nauseum.
So you're declaring:
-"At any time" isn't actually at any time -A rule that hasn't changed between 2014 and 2024 has somehow changed without any errata telling us so
Definitely incorrect on both counts. Especially when we have this correct statement:
However, if we're discussing the visibility of subtle spellcasting: 2024 doesn't say, and therefore we can just rely on XGTE, because they were never overridden and, as has been stated many times, 2024 edition is still 5e.
Moving and Communicating take no actions but are still restricted to your turn. Ending Concentration requires no action to end on your turn. Nothing allows you to end Concentration as a non action outside of your turn. A spellcaster (any spellcaster in a Circle spell) can abort the casting at any time that they are eligible to end Concentration, which is only on their turn.
I didn't.
I have explained it multiple times already. If you do not understand the words I wrote that is one thing. If you do not agree with me and expect that by starting with the declaration that I am incorrect, I will magically buckle, I won't. Until we get a Sage Advice or Errata, I am correct. Until then, you are also correct. We both have valid readings. I will absolutely not back down from my reading being valid, but I will not declare yours invalid. I do not care intensely, what direction WotC chooses, only that they officially clarify their rules. Please, select another area of the conversation where I won't be repeating myself ad nauseum.
So you're declaring:
-"At any time" isn't actually at any time
No. That's fair. I was focused on the No Action Required.
It doesn't really change anything since if the spell is being cast with V, S, M components, it is being cast with V, S, M components until it is completed or aborted. The fact that you can abort the casting provides no evidence that casting a spell is restricted to during the Magic action you used to cast or continue casting it.
-A rule that hasn't changed between 2014 and 2024 has somehow changed without any errata telling us so
The trigger for Counterspell changed from 2024 and so did the possible interpretations. You are welcome to make an RAI argument based on the XGtE, but not a RAW one. Even if you consider XGtE currently applicable to the 2024 rules, the specific trigger of Counterspell 2024 would override the general rules of Xanathar's. It's not relevant.
The trigger for Counterspell changed from 2024 and so did the possible interpretations.
The trigger for counterspell in 2024 was changed to make it explicit that you must be able to tell that the creature is casting a spell, whereas in 2014 it was merely implicit.
The trigger for Counterspell changed from 2024 and so did the possible interpretations.
The trigger for counterspell in 2024 was changed to make it explicit that you must be able to tell that the creature is casting a spell, whereas in 2014 it was merely implicit.
That is your opinion and I am not contesting the validity of it, but unless your next steps are going to be to update the Sage Advice, it will just be your opinion.
Do you have anything new to add or is this just going to a game of "I'm right and your wrong"? I have defended the validity of my position multiple times. You are not required to agree with it for it to be a valid reading. If we are discussing a spell cast by a single caster, there is no practical difference in our interpretations (unless you subscribe to the belief that Counterspell can only cast as a reaction in response to the casting creature's Magic action). Only when we have multiple casters do we differ. This is a scenario, that did not exist in 2014 and was created while Jeremy Crawford was lead and, without knowing how much the 5.24 supplemental products overlapped with the original core books in development/planning, could have been explicitly taken into account when updating Counterspell. There is no way for us to know.
The secondary casters are also casters of the Circle spell. If the Circle spell is being cast with Verbal, Somatic, and Material components and you can see the secondary casters, they are a creature you see casting a spell with Verbal, Somatic, and Material components. If they are within 60 feet, you can Counterspell the Circle spell by targeting the secondary casters.
I will be happy to see it clarified as I am wrong. I will be happy to see it clarified as I am correct. I will be happy to see it clarified.
Do you have anything new to add or is this just going to a game of "I'm right and your wrong"? I have defended the validity of my position multiple times.
No, you've ignored everyone who pointed out your reading didn't match the actual language, broke the clauses up in funny ways rather than reading them all together, and that the 2024 reaction condition really does require that you see components being used by the creature you're targeting.
It doesn't really change anything since if the spell is being cast with V, S, M components, it is being cast with V, S, M components until it is completed or aborted.
This is actually false. It is only being cast with VSM components while the main caster is taking a magic action, because they're the ones doing the V, S, and M, and they only get to act on their turn when not taking a reaction.
Moving and Communicating take no actions but are still restricted to your turn. Ending Concentration requires no action to end on your turn. Nothing allows you to end Concentration as a non action outside of your turn. A spellcaster (any spellcaster in a Circle spell) can abort the casting at any time that they are eligible to end Concentration, which is only on their turn.
I don't know where you read that Concentration can only end on your turn , it instead say, at any time, meaning on anyone's turn. Further limitation is on you.
Moving and Communicating take no actions but are still restricted to your turn. Ending Concentration requires no action to end on your turn. Nothing allows you to end Concentration as a non action outside of your turn. A spellcaster (any spellcaster in a Circle spell) can abort the casting at any time that they are eligible to end Concentration, which is only on their turn.
I don't know where you read that Concentration can only end on your turn , it instead say, at any time, meaning on anyone's turn. Further limitation is on you.
No. That's fair. I was focused on the No Action Required.
It doesn't really change anything since if the spell is being cast with V, S, M components, it is being cast with V, S, M components until it is completed or aborted. The fact that you can abort the casting provides no evidence that casting a spell is restricted to during the Magic action you used to cast or continue casting it
You are misreading that. They say that the Reaction also Triggers in this case. That means that this particular moment is an additional Trigger. The statement does nothing to remove the Reaction's original trigger.
Sure, the original trigger remains. But that doesn't have to mean that the original trigger can trigger on the event that the additional trigger responds to.
In essence, what they are establishing is that, yes, the act of being primary caster is essentially one of 'casting a spell' and we aren't suppose to try and argue 'well, they're taking the Magic action, but the spell requires the contribution of a group, so they aren't actually 'casting'.'
Absolutely not. It does not define initiation a Circle spell as casting a spell, if it did it would say so (which it doesn't do). But you are correct on the fact that we don't need to argue about if they are casting or not because the new trigger they defined for us will work anyway.
I did not say that they define it that way. I said that it was 'in essence' (i.e., there is an implication that it is functioning that way, even though they do not define it that way).
I disagree that they fact that the did not state something means that isn't the intent. A very common argument when dealing with 'RAW' is 'they don't need to state every single individual thing, just exceptions'. I'm not saying your argument is completely invalid, but we are definitely in the realm of alternative interpretations
And yes, I recognize the irony of taking this position since I was earlier arguing that there was nothing implying you couldn't extend a casting action, but that was my point, until people found and pointed out rules, I literally could find nothing saying that. The fact that Counterspell appears to be written to allow it to be triggered after the initial action to begin a spell with a casting duration of over 1 turn is, at least, something.
Now, as I said, this isn't meant to be a statement of 'you are definitively wrong'. The wording doesn't support that. However, I would, and definitely will, argue that barring some form of clarification, either as a rule or as a statement by designers, interpreting the primary caster as 'casting' from the time of their first action until the final secondary caster contributes and the spell is 'released' (in the case of a single action spell) is a reasonable interpretation. No, it is not Black Letter RAW, but it is very easy to see how people come to the decision that this is within the rules and I do not see anything in the rules that clearly defines that interpretation as being incorrect.
In practice, I have trouble coming up with a scenario where counterspelling a circle spell is at all likely, because you have to be within 90' and have clear line of sight on the caster, and if you were already in position... all you have to do is break someone's concentration, either with bulk damage or incapacitating status effects, and that's much easier than getting off a counterspell. . .
So, this does bring us into a rather messy area concerning Circle Magic. As written, and pretty clearly so, secondary casters do not need to maintain Concentration on any spell with a casting time of only 1 Action. That requirement is explicitly stated to occur only when a spell has a casting time of 1 minute or more. My earliest arguments were predicated on a period of time that was fairly clearly between 1 Round and 1 minute (i.e., extending the casting time to longer than a single Round), but since that is not a possibility, the explicit RAW seems to be pretty clear.
My personal interpretation is that for such a 'fast' spell, the secondary casters just put in a lump sum of energy that the caster is then able to hold onto for a very brief amount of time and then shape. It is more akin to giving something a shove than carrying something. As result, after they have contributed they no longer need to maintain Concentration. They don't even need to remain alive since, with how the Black Letter RAW is written, they could even die without disrupting the spell. (My interpretation is that they contribute a 'lump' of energy. The lack of Concentration is not my interpretation but simply appears to be RAW and RAI).
Again, and for clarity, this is only when spells have a casting time of less than 1 minute, which as of this moment equates to casting times of 1 Action since there are currently no significant options in between those two, outside of Circle Magic on a 1 Action spell, and that only extends a slight bit out of 1 Action.
(and for the record, I really think the designers should adjust the rules to future-proof them, just in case a situation occurs at some later date where a spell, for some reason, takes multiple Rounds but still less than 1 Minute)
So, this does bring us into a rather messy area concerning Circle Magic. As written, and pretty clearly so, secondary casters do not need to maintain Concentration on any spell with a casting time of only 1 Action.
Hm. I actually missed that it was even usable on single action spells when I first read through the rules. Yeah, that's a bit of a mess, but honestly, all of circle magic is a mess (yes, it's useful to have plot device group ritual spells, but that doesn't mean it's necessary to actually provide rules for them, and the rules should probably be set up to make circle magic relatively easily countered by a small band of heroes...).
So, this does bring us into a rather messy area concerning Circle Magic. As written, and pretty clearly so, secondary casters do not need to maintain Concentration on any spell with a casting time of only 1 Action. That requirement is explicitly stated to occur only when a spell has a casting time of 1 minute or more.
I would agree that it is RAW.
I wouldn't say that it is clearly written as such. Secondary casters are explicitly written as needing to maintain concentration until the spell completes if the spell has a casting time of longer than 1 action. It is stated as part of needing to repeat the Magic action. For 1 action spells, it is stated that the spell effects occur after the last Magic action from the secondary casters. Because there is no need for a reminder to repeat a Magic action, it is possible that the secondary caster concentration requirement was omitted in error.
If it explicitly said the secondary casters did not need to maintain concentration, it would be clearly written. Normally saying concentration is not required wouldn't be necessary but with the inconsistency with longer casting times, I feel there is a decent chance that it was in error. I think that RAI is that they need to maintain concentration, but I am labelling it as a house rule.
Choosing to gate any mention of Concentration for secondary casters behind the "1 minute or more" part should be pretty clear to anyone reading it normally. It takes someone intentionally looking for any way to twist or misunderstand the rules to believe otherwise.
So, this does bring us into a rather messy area concerning Circle Magic. As written, and pretty clearly so, secondary casters do not need to maintain Concentration on any spell with a casting time of only 1 Action. That requirement is explicitly stated to occur only when a spell has a casting time of 1 minute or more.
I would agree that it is RAW.
I wouldn't say that it is clearly written as such. Secondary casters are explicitly written as needing to maintain concentration until the spell completes if the spell has a casting time of longer than 1 action. It is stated as part of needing to repeat the Magic action. For 1 action spells, it is stated that the spell effects occur after the last Magic action from the secondary casters. Because there is no need for a reminder to repeat a Magic action, it is possible that the secondary caster concentration requirement was omitted in error.
If it explicitly said the secondary casters did not need to maintain concentration, it would be clearly written. Normally saying concentration is not required wouldn't be necessary but with the inconsistency with longer casting times, I feel there is a decent chance that it was in error. I think that RAI is that they need to maintain concentration, but I am labelling it as a house rule.
No. Secondary casters are explicitly written as being required to maintain Concentration on any spell with a casting time of 1 minute or more, not 'longer than 1 action'.
If it was possible for the secondary casters to need to repeat the Magic Action during the casting of a 1 Action spell being cast through Circle Magic, then yes, I would support the argument that maybe Concentration needs to be maintained and the problem is this undefined area that exists between 1 Action and 1 Minute. However, that does not happen. It is explicitly stated, in Circle Magic, that all secondary casters must contribute before the primary caster's next turn. That means, barring some edge cases that could be created by a person readying an action to contribute, they will not usually get another Action before all contributions are completed.
So now we are pretty clearly in the area that it seems that the writers did not intend for Concentration until the spell is cast to be a requirement for these shorter spells. There is no real potential for the casting time to be significantly increased, so the 'undefined country' exists very close to the '1 Action' country. Given that, it does not seem appropriate to be trying to apply the rules for an area that is much further away instead of using the rules for '1 Action'.
I should note, I was previously in the same camp as you, arguing that Concentration needed to be maintained the entire time since I believed it was possible for a Circle Magic casting to take multiple rounds and was rather vociferous in arguing against people who were simply claiming 'it doesn't work that way'. It was only when I was presented with actual rules that pretty strongly indicated that the casting time could not be significantly extended that I modified my position.
I now use a 'head canon' that has the secondary casters contributing a 'lump' of energy to the primary casters in these cases, and then they are out. They still need to maintain Concentration for spells with a casting time of 1 minute or more, but for the single action spells this concept seems to conform to the Rules as Written.
No. Secondary casters are explicitly written as being required to maintain Concentration on any spell with a casting time of 1 minute or more, not 'longer than 1 action'.
Show me a spell with a casting time greater than 1 action but less than 1 minute that is eligible to be cast a circle spell. Maybe I have forgotten one exists in 5e.
I should note, I was previously in the same camp as you, arguing that Concentration needed to be maintained the entire time since I believed it was possible for a Circle Magic casting to take multiple rounds and was rather vociferous in arguing against people who were simply claiming 'it doesn't work that way'. It was only when I was presented with actual rules that pretty strongly indicated that the casting time could not be significantly extended that I modified my position.
I am not making either of those arguments. I am only making the argument that the intention regarding maintaining concentration is not as clear as claimed.
Choosing to gate any mention of Concentration for secondary casters behind the "1 minute or more" part should be pretty clear to anyone reading it normally. It takes someone intentionally looking for any way to twist or misunderstand the rules to believe otherwise.
That is RAW but it creates an inconsistency where under one scenario, secondary casters must also maintain concentration from when they contribute to the spell until the Circle spell is complete and another where they do not. Because they mention it under the scenario of repeating the Magic action, it is potentially an unintended omission. Therefore, RAI is not certain.
Moving and Communicating take no actions but are still restricted to your turn. Ending Concentration requires no action to end on your turn. Nothing allows you to end Concentration as a non action outside of your turn. A spellcaster (any spellcaster in a Circle spell) can abort the casting at any time that they are eligible to end Concentration, which is only on their turn.
I didn't.
I have explained it multiple times already. If you do not understand the words I wrote that is one thing. If you do not agree with me and expect that by starting with the declaration that I am incorrect, I will magically buckle, I won't. Until we get a Sage Advice or Errata, I am correct. Until then, you are also correct. We both have valid readings. I will absolutely not back down from my reading being valid, but I will not declare yours invalid. I do not care intensely, what direction WotC chooses, only that they officially clarify their rules. Please, select another area of the conversation where I won't be repeating myself ad nauseum.
Initiating a Circle spell and contributing to one are both steps under Casting a Circle Spell. Cast a Circle spell follows rules for spellcasting in the PHB and also the rules for Circle spells. That said, I personally have less of an issue with saying that none of the spellcasters are casting a spell as opposed to only the primary caster is. In your view, I suppose the only opportunities for triggers when a spell is cast would be when the Circle spell is initiated (due the explicit call out) and when the spell completes (this would apply to an Arcane Trickster's Spell Thief and Order Domain's Voice of Authority)?
How to add Tooltips.
My houserulings.
So you're declaring:
-"At any time" isn't actually at any time
-A rule that hasn't changed between 2014 and 2024 has somehow changed without any errata telling us so
Definitely incorrect on both counts. Especially when we have this correct statement:
No. That's fair. I was focused on the No Action Required.
It doesn't really change anything since if the spell is being cast with V, S, M components, it is being cast with V, S, M components until it is completed or aborted. The fact that you can abort the casting provides no evidence that casting a spell is restricted to during the Magic action you used to cast or continue casting it.
The trigger for Counterspell changed from 2024 and so did the possible interpretations. You are welcome to make an RAI argument based on the XGtE, but not a RAW one. Even if you consider XGtE currently applicable to the 2024 rules, the specific trigger of Counterspell 2024 would override the general rules of Xanathar's. It's not relevant.
How to add Tooltips.
My houserulings.
The trigger for counterspell in 2024 was changed to make it explicit that you must be able to tell that the creature is casting a spell, whereas in 2014 it was merely implicit.
That is your opinion and I am not contesting the validity of it, but unless your next steps are going to be to update the Sage Advice, it will just be your opinion.
Do you have anything new to add or is this just going to a game of "I'm right and your wrong"? I have defended the validity of my position multiple times. You are not required to agree with it for it to be a valid reading. If we are discussing a spell cast by a single caster, there is no practical difference in our interpretations (unless you subscribe to the belief that Counterspell can only cast as a reaction in response to the casting creature's Magic action). Only when we have multiple casters do we differ. This is a scenario, that did not exist in 2014 and was created while Jeremy Crawford was lead and, without knowing how much the 5.24 supplemental products overlapped with the original core books in development/planning, could have been explicitly taken into account when updating Counterspell. There is no way for us to know.
The secondary casters are also casters of the Circle spell. If the Circle spell is being cast with Verbal, Somatic, and Material components and you can see the secondary casters, they are a creature you see casting a spell with Verbal, Somatic, and Material components. If they are within 60 feet, you can Counterspell the Circle spell by targeting the secondary casters.
I will be happy to see it clarified as I am wrong. I will be happy to see it clarified as I am correct. I will be happy to see it clarified.
How to add Tooltips.
My houserulings.
No, you've ignored everyone who pointed out your reading didn't match the actual language, broke the clauses up in funny ways rather than reading them all together, and that the 2024 reaction condition really does require that you see components being used by the creature you're targeting.
Your position is obviously invalid.
This is actually false. It is only being cast with VSM components while the main caster is taking a magic action, because they're the ones doing the V, S, and M, and they only get to act on their turn when not taking a reaction.
I don't know where you read that Concentration can only end on your turn , it instead say, at any time, meaning on anyone's turn. Further limitation is on you.
See below.
How to add Tooltips.
My houserulings.
I did not say that they define it that way. I said that it was 'in essence' (i.e., there is an implication that it is functioning that way, even though they do not define it that way).
I disagree that they fact that the did not state something means that isn't the intent. A very common argument when dealing with 'RAW' is 'they don't need to state every single individual thing, just exceptions'. I'm not saying your argument is completely invalid, but we are definitely in the realm of alternative interpretations
And yes, I recognize the irony of taking this position since I was earlier arguing that there was nothing implying you couldn't extend a casting action, but that was my point, until people found and pointed out rules, I literally could find nothing saying that. The fact that Counterspell appears to be written to allow it to be triggered after the initial action to begin a spell with a casting duration of over 1 turn is, at least, something.
Now, as I said, this isn't meant to be a statement of 'you are definitively wrong'. The wording doesn't support that. However, I would, and definitely will, argue that barring some form of clarification, either as a rule or as a statement by designers, interpreting the primary caster as 'casting' from the time of their first action until the final secondary caster contributes and the spell is 'released' (in the case of a single action spell) is a reasonable interpretation. No, it is not Black Letter RAW, but it is very easy to see how people come to the decision that this is within the rules and I do not see anything in the rules that clearly defines that interpretation as being incorrect.
So, this does bring us into a rather messy area concerning Circle Magic. As written, and pretty clearly so, secondary casters do not need to maintain Concentration on any spell with a casting time of only 1 Action. That requirement is explicitly stated to occur only when a spell has a casting time of 1 minute or more. My earliest arguments were predicated on a period of time that was fairly clearly between 1 Round and 1 minute (i.e., extending the casting time to longer than a single Round), but since that is not a possibility, the explicit RAW seems to be pretty clear.
My personal interpretation is that for such a 'fast' spell, the secondary casters just put in a lump sum of energy that the caster is then able to hold onto for a very brief amount of time and then shape. It is more akin to giving something a shove than carrying something. As result, after they have contributed they no longer need to maintain Concentration. They don't even need to remain alive since, with how the Black Letter RAW is written, they could even die without disrupting the spell. (My interpretation is that they contribute a 'lump' of energy. The lack of Concentration is not my interpretation but simply appears to be RAW and RAI).
Again, and for clarity, this is only when spells have a casting time of less than 1 minute, which as of this moment equates to casting times of 1 Action since there are currently no significant options in between those two, outside of Circle Magic on a 1 Action spell, and that only extends a slight bit out of 1 Action.
(and for the record, I really think the designers should adjust the rules to future-proof them, just in case a situation occurs at some later date where a spell, for some reason, takes multiple Rounds but still less than 1 Minute)
Hm. I actually missed that it was even usable on single action spells when I first read through the rules. Yeah, that's a bit of a mess, but honestly, all of circle magic is a mess (yes, it's useful to have plot device group ritual spells, but that doesn't mean it's necessary to actually provide rules for them, and the rules should probably be set up to make circle magic relatively easily countered by a small band of heroes...).
I would agree that it is RAW.
I wouldn't say that it is clearly written as such. Secondary casters are explicitly written as needing to maintain concentration until the spell completes if the spell has a casting time of longer than 1 action. It is stated as part of needing to repeat the Magic action. For 1 action spells, it is stated that the spell effects occur after the last Magic action from the secondary casters. Because there is no need for a reminder to repeat a Magic action, it is possible that the secondary caster concentration requirement was omitted in error.
If it explicitly said the secondary casters did not need to maintain concentration, it would be clearly written. Normally saying concentration is not required wouldn't be necessary but with the inconsistency with longer casting times, I feel there is a decent chance that it was in error. I think that RAI is that they need to maintain concentration, but I am labelling it as a house rule.
How to add Tooltips.
My houserulings.
Choosing to gate any mention of Concentration for secondary casters behind the "1 minute or more" part should be pretty clear to anyone reading it normally. It takes someone intentionally looking for any way to twist or misunderstand the rules to believe otherwise.
No. Secondary casters are explicitly written as being required to maintain Concentration on any spell with a casting time of 1 minute or more, not 'longer than 1 action'.
If it was possible for the secondary casters to need to repeat the Magic Action during the casting of a 1 Action spell being cast through Circle Magic, then yes, I would support the argument that maybe Concentration needs to be maintained and the problem is this undefined area that exists between 1 Action and 1 Minute. However, that does not happen. It is explicitly stated, in Circle Magic, that all secondary casters must contribute before the primary caster's next turn. That means, barring some edge cases that could be created by a person readying an action to contribute, they will not usually get another Action before all contributions are completed.
So now we are pretty clearly in the area that it seems that the writers did not intend for Concentration until the spell is cast to be a requirement for these shorter spells. There is no real potential for the casting time to be significantly increased, so the 'undefined country' exists very close to the '1 Action' country. Given that, it does not seem appropriate to be trying to apply the rules for an area that is much further away instead of using the rules for '1 Action'.
I should note, I was previously in the same camp as you, arguing that Concentration needed to be maintained the entire time since I believed it was possible for a Circle Magic casting to take multiple rounds and was rather vociferous in arguing against people who were simply claiming 'it doesn't work that way'. It was only when I was presented with actual rules that pretty strongly indicated that the casting time could not be significantly extended that I modified my position.
I now use a 'head canon' that has the secondary casters contributing a 'lump' of energy to the primary casters in these cases, and then they are out. They still need to maintain Concentration for spells with a casting time of 1 minute or more, but for the single action spells this concept seems to conform to the Rules as Written.
Show me a spell with a casting time greater than 1 action but less than 1 minute that is eligible to be cast a circle spell. Maybe I have forgotten one exists in 5e.
I am not making either of those arguments. I am only making the argument that the intention regarding maintaining concentration is not as clear as claimed.
That is RAW but it creates an inconsistency where under one scenario, secondary casters must also maintain concentration from when they contribute to the spell until the Circle spell is complete and another where they do not. Because they mention it under the scenario of repeating the Magic action, it is potentially an unintended omission. Therefore, RAI is not certain.
How to add Tooltips.
My houserulings.