Op. Conditioning (Concat)

This is ComfyUI's Conditioning (Concat) with the guardrails off - or rather, with a guardrail added: both of its inputs are optional, so it won't crash when one of them is missing. It joins two CONDITIONING inputs into one, and if you only give it one (or neither), it just passes through what it has instead of erroring.

Why you'd reach for it

Concatenating conditioning is how you glue prompts together end to end - it appends one set of prompt tokens after another, which is different from combining (averaging) them. It's a normal thing to want: a base style prompt plus a per-shot subject prompt, stacked.

The reason for the "optional" version is conditional workflows. Stock Conditioning (Concat) requires both inputs, so the moment one branch is muted or a source isn't connected, the graph breaks. OptionalConditioningConcat is built for exactly that situation: wire in a conditioning that may or may not be present, and the node handles the missing case gracefully by passing through whatever it does have. That makes it a clean building block for toggleable prompt sections - turn a branch off and the concat just becomes a pass-through instead of a failure. It's the same "don't fall over when a slot is empty" philosophy behind the pack's other optional nodes.

How it works

Both inputs are optional CONDITIONING. If both are present, it concatenates them (conditioning_from appended onto conditioning_to) and outputs the result. If only one is present, it outputs that one unchanged. The output is always a single CONDITIONING, so downstream nodes get something valid regardless of which branches were live.

The inputs and outputs

• conditioning_to (optional) - the base conditioning that the other gets appended to.
• conditioning_from (optional) - the conditioning appended onto conditioning_to.

The output is a single CONDITIONING - the concatenation, or whichever input was present.

Installing it

ComfyUI Manager → search antrobots ComfyUI Nodepack, install, restart. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/antrobot1234/antrobots-comfyUI-nodepack

No models or dependencies - it operates on conditioning tensors.

Common issues

Keep the mental model straight: this concatenates (appends tokens end to end), it does not combine (average two conditionings for a blended effect). If you wanted the two prompts blended rather than sequenced, you want ComfyUI's Conditioning (Combine), not this. Using concat where you meant combine tends to over-weight the later prompt in a way people find surprising.

Second, order matters. conditioning_from is appended onto conditioning_to, and prompt order affects the result, so if the emphasis feels off, try swapping which conditioning goes into which slot.

And the happy failure mode is worth restating so you don't misread it: if you expected a concatenation but got just one prompt's worth of conditioning, that's the node telling you one of its inputs was empty. It didn't error because it's designed not to - check whether the branch you thought was feeding it is actually connected and unmuted.