Claude is quite bad at following instructions compared to other SOTA models.
As in, you tell it "only answer with a number", then it proceeds to tell you "13, I chose that number because..."
As in, you tell it "only answer with a number", then it proceeds to tell you "13, I chose that number because..."
[1] Reinforcement learning from human feedback; basically participants got two model responses and had to judge them on multiple criteria relative to the prompt
I suspect in part because the provider also didn't want to create an easy cop out for the people working on the fine-tuning part (a lot of my work was auditing and reviewing output, and there was indeed a lot of really sloppy work, up to and including cut and pasting output from other LLMs - we know, because on more than one occasion I caught people who had managed to include part of Claudes website footer in their answer...)
I upgraded to a new model (gpt-4o-mini to grok-4.1-fast), suddenly all my workflows were broken. I was like "this new model is shit!", then I looked into my prompts and realized the model was actually better at following instructions, and my instructions were wrong/contradictory.
After I fixed my prompts it did exactly what I asked for.
Maybe models should have another tuneable parameters, on how well it should respect the user prompt. This reminds me of imagegen models, where you can choose the config/guidance scale/diffusion strength.
Claude is now actually one of the better ones at instruction following I daresay.
For example, sometimes it outputs in markdown, without being asked to (e.g. "**13**" instead of "13"), even when asked to respond with a number only.
This might be fine in a chat-environment, but not in a workflow, agentic use-case or tool usage.
Yes, it can be enforced via structured output, but in a string field from a structured output you might still want to enforce a specific natural-language response format, which can't be defined by a schema.