Can you use SD1.5 LoRAs / ControlNets with SDXL?

Short answer: no, you can't. And this isn't just about SD1.5 and SDXL. It's safe to assume that different models are almost never compatible with each other.

Think of it like power outlets.

  • SD1.5 is a Japanese outlet (Type A)
  • SDXL is a US outlet (Type B)

Appliances (LoRA / ControlNet) made for one country only work in that country. They may do similar things, but the plugs are shaped differently, so they physically won't fit.

Why aren't they compatible?

Roughly speaking, the technical reasons are:

  • They are built for different models

    • SD1.5 and SDXL have different UNet structures, channel counts, latent resolutions, etc., so the assumption a LoRA / ControlNet relies on, "which layer gets which difference added", no longer holds.

  • Text encoders are also different

    • SD1.5 uses CLIP, while SDXL uses a text encoder with a different configuration. What was learned about "how this word should shift the result" doesn't carry over to a different model.

It's fine to think of an adapter as working only with the model it was made for.

  • LoRA / ControlNet for SD1.5 → SD1.5-family models only
  • LoRA / ControlNet for SDXL → SDXL-family models only
  • LoRA / ControlNet for Flux → Flux-family models only

Do you actually get an error?

If you plug an SDXL ControlNet model into an SD1.5 ControlNet workflow, you get an error like the one above:

y is None, did you try using a controlnet for SDXL on SD1?

So ComfyUI itself detects the mismatch and returns an error.